chore(thumbnails): change default executor

docs/docs/installation/cache.mdx

@@ -87,13 +87,16 @@ FEATURE_FLAGS = {
 }
 ```
 
-By default thumbnails are rendered using the `THUMBNAIL_SELENIUM_USER` user account. To render thumbnails as the
-logged in user (e.g. in environments that are using user impersonation), use the following configuration:
+By default thumbnails are rendered per user. To render thumbnails as a fixed user (`admin` in this example), use the following configuration:
 
 ```python
-THUMBNAIL_EXECUTE_AS = [ExecutorType.CURRENT_USER]
+from superset.tasks.types import ExecutorType
+
+THUMBNAIL_SELENIUM_USER = "admin"
+THUMBNAIL_EXECUTE_AS = [ExecutorType.SELENIUM]
 ```
 
+
 For this feature you will need a cache system and celery workers. All thumbnails are stored on cache
 and are processed asynchronously by the workers.
 

superset/config.py

@@ -611,16 +611,13 @@ def _try_json_readsha(filepath: str, length: int) -> Optional[str]:
 # ---------------------------------------------------
 # Thumbnail config (behind feature flag)
 # ---------------------------------------------------
-# When executing Alerts & Reports or Thumbnails as the Selenium user, this defines
-# the username of the account used to render the queries and dashboards/charts
+# By default, thumbnails are rendered per user. Similar to Alerts & Reports, thumbnails
+# can be configured to be rendered as a fixed user. See
+# `superset.tasks.types.ExecutorType` for a full list of executor options.
+# To use a fixed user account, use the following configuration:
+# THUMBNAIL_EXECUTE_AS = [ExecutorType.SELENIUM]
 THUMBNAIL_SELENIUM_USER: Optional[str] = "admin"
-
-# To be able to have different thumbnails for different users, use these configs to
-# define which user to execute the thumbnails and potentially custom functions for
-# calculating thumbnail digests. To have unique thumbnails for all users, use the
-# following config:
-# THUMBNAIL_EXECUTE_AS = [ExecutorType.CURRENT_USER]
-THUMBNAIL_EXECUTE_AS = [ExecutorType.SELENIUM]
+THUMBNAIL_EXECUTE_AS = [ExecutorType.CURRENT_USER]
 
 # By default, thumbnail digests are calculated based on various parameters in the
 # chart/dashboard metadata, and in the case of user-specific thumbnails, the