Add serverless_compute_id field to the config (#685)

## Changes
We propose adding a new `serverless_compute_id` attribute in the config
that will be used to enable serverless compute in the downstream
applications. The default value to enable serverless is
`serverless_compute_id = auto`, other values might be used in the future
if needed. Config doesn't have to validate the value in
`serverless_compute_id`, this will be done in the downstream
applications.

## Tests

- [x] `make test` run locally
- [x] `make fmt` applied
- [ ] relevant integration tests applied

databricks/sdk/config.py

@@ -66,6 +66,7 @@ class Config:
     auth_type: str = ConfigAttribute(env='DATABRICKS_AUTH_TYPE')
     cluster_id: str = ConfigAttribute(env='DATABRICKS_CLUSTER_ID')
     warehouse_id: str = ConfigAttribute(env='DATABRICKS_WAREHOUSE_ID')
+    serverless_compute_id: str = ConfigAttribute(env='DATABRICKS_SERVERLESS_COMPUTE_ID')
     skip_verify: bool = ConfigAttribute()
     http_timeout_seconds: float = ConfigAttribute()
     debug_truncate_bytes: int = ConfigAttribute(env='DATABRICKS_DEBUG_TRUNCATE_BYTES')