Revise DATABRICKS_API_TOKEN as DATABRICKS_TOKEN (langchain-ai#5796)

<!--
Thank you for contributing to LangChain! Your PR will appear in our
release under the title you set. Please make sure it highlights your
valuable contribution.

Replace this with a description of the change, the issue it fixes (if
applicable), and relevant context. List any dependencies required for
this change.

After you're done, someone will review your PR. They may suggest
improvements. If no one reviews your PR within a few days, feel free to
@-mention the same people again, as notifications can get lost.

Finally, we'd love to show appreciation for your contribution - if you'd
like us to shout you out on Twitter, please also include your handle!
-->

In the [Databricks
integration](https://python.langchain.com/en/latest/integrations/databricks.html)
and [Databricks
LLM](https://python.langchain.com/en/latest/modules/models/llms/integrations/databricks.html),
we suggestted users to set the ENV variable `DATABRICKS_API_TOKEN`.
However, this is inconsistent with the other Databricks library. To make
it consistent, this PR changes the variable from `DATABRICKS_API_TOKEN`
to `DATABRICKS_TOKEN`

After changes, there is no more `DATABRICKS_API_TOKEN` in the doc
```
$ git grep DATABRICKS_API_TOKEN|wc -l
0

$ git grep DATABRICKS_TOKEN|wc -l
8
```
cc @hwchase17 @dev2049 @mengxr since you have reviewed the previous PRs.

docs/integrations/databricks.ipynb

@@ -58,7 +58,7 @@
     "### Optional Parameters\n",
     "There following parameters are optional. When executing the method in a Databricks notebook, you don't need to provide them in most of the cases.\n",
     "* `host`: The Databricks workspace hostname, excluding 'https://' part. Defaults to 'DATABRICKS_HOST' environment variable or current workspace if in a Databricks notebook.\n",
-    "* `api_token`: The Databricks personal access token for accessing the Databricks SQL warehouse or the cluster. Defaults to 'DATABRICKS_API_TOKEN' environment variable or a temporary one is generated if in a Databricks notebook.\n",
+    "* `api_token`: The Databricks personal access token for accessing the Databricks SQL warehouse or the cluster. Defaults to 'DATABRICKS_TOKEN' environment variable or a temporary one is generated if in a Databricks notebook.\n",
     "* `warehouse_id`: The warehouse ID in the Databricks SQL.\n",
     "* `cluster_id`: The cluster ID in the Databricks Runtime. If running in a Databricks notebook and both 'warehouse_id' and 'cluster_id' are None, it uses the ID of the cluster the notebook is attached to.\n",
     "* `engine_args`: The arguments to be used when connecting Databricks.\n",

docs/modules/models/llms/integrations/databricks.ipynb

@@ -163,14 +163,14 @@
    ],
    "source": [
     "# Otherwise, you can manually specify the Databricks workspace hostname and personal access token \n",
-    "# or set `DATABRICKS_HOST` and `DATABRICKS_API_TOKEN` environment variables, respectively.\n",
+    "# or set `DATABRICKS_HOST` and `DATABRICKS_TOKEN` environment variables, respectively.\n",
     "# See https://docs.databricks.com/dev-tools/auth.html#databricks-personal-access-tokens\n",
     "# We strongly recommend not exposing the API token explicitly inside a notebook.\n",
     "# You can use Databricks secret manager to store your API token securely.\n",
     "# See https://docs.databricks.com/dev-tools/databricks-utils.html#secrets-utility-dbutilssecrets\n",
     "\n",
     "import os\n",
-    "os.environ[\"DATABRICKS_API_TOKEN\"] = dbutils.secrets.get(\"myworkspace\", \"api_token\")\n",
+    "os.environ[\"DATABRICKS_TOKEN\"] = dbutils.secrets.get(\"myworkspace\", \"api_token\")\n",
     "\n",
     "llm = Databricks(host=\"myworkspace.cloud.databricks.com\", endpoint_name=\"dolly\")\n",
     "\n",

langchain/llms/databricks.py

@@ -114,7 +114,7 @@ def get_default_api_token() -> str:
     """Gets the default Databricks personal access token.
     Raises an error if the token cannot be automatically determined.
     """
-    if api_token := os.getenv("DATABRICKS_API_TOKEN"):
+    if api_token := os.getenv("DATABRICKS_TOKEN"):
         return api_token
     try:
         api_token = get_repl_context().apiToken
@@ -123,7 +123,7 @@ def get_default_api_token() -> str:
     except Exception as e:
         raise ValueError(
             "api_token was not set and cannot be automatically inferred. Set "
-            f"environment variable 'DATABRICKS_API_TOKEN'. Received error: {e}"
+            f"environment variable 'DATABRICKS_TOKEN'. Received error: {e}"
         )
     # TODO: support Databricks CLI profile
     return api_token
@@ -186,7 +186,7 @@ class Databricks(LLM):
     """Databricks personal access token.
     If not provided, the default value is determined by
 
-    * the ``DATABRICKS_API_TOKEN`` environment variable if present, or
+    * the ``DATABRICKS_TOKEN`` environment variable if present, or
     * an automatically generated temporary token if running inside a Databricks
       notebook attached to an interactive cluster in "single user" or
       "no isolation shared" mode.

langchain/sql_database.py

@@ -150,7 +150,7 @@ def from_databricks(
                 hostname. Defaults to None.
             api_token (Optional[str]): The Databricks personal access token for
                 accessing the Databricks SQL warehouse or the cluster. If not provided,
-                it attempts to fetch from 'DATABRICKS_API_TOKEN'. If still unavailable
+                it attempts to fetch from 'DATABRICKS_TOKEN'. If still unavailable
                 and running in a Databricks notebook, a temporary token for the current
                 user is generated. Defaults to None.
             warehouse_id (Optional[str]): The warehouse ID in the Databricks SQL. If
@@ -197,7 +197,7 @@ def from_databricks(
         default_api_token = context.apiToken if context else None
         if api_token is None:
             api_token = utils.get_from_env(
-                "api_token", "DATABRICKS_API_TOKEN", default_api_token
+                "api_token", "DATABRICKS_TOKEN", default_api_token
             )
 
         if warehouse_id is None and cluster_id is None: