[Feature] Customize and document event_log block in databricks_pipeline (#4612)

## Changes
<!-- Summary of your changes that are easy to understand -->

The only required parameter is `event_log.name`, the `catalog` and
`schema` are inherited from the pipeline settings.

## Tests
<!-- 
How is this tested? Please see the checklist below and also describe any
other relevant tests
-->

- [x] `make test` run locally
- [x] relevant change in `docs/` folder
- [ ] covered with integration tests in `internal/acceptance`
- [ ] using Go SDK
- [ ] using TF Plugin Framework

Author: alexott

NEXT_CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### New Features and Improvements
 
+ * Customize and document `event_log` block in `databricks_pipeline` ([#4612](https://github.com/databricks/terraform-provider-databricks/pull/4612))
  * Add automatic clustering support for `databricks_sql_table` ([#4607](https://github.com/databricks/terraform-provider-databricks/pull/4607))
 
 ### Bug Fixes

docs/resources/pipeline.md

@@ -97,7 +97,10 @@ The following arguments are supported:
   * `gateway_storage_catalog` - Required, Immutable. The name of the catalog for the gateway pipeline's storage location.
   * `gateway_storage_name` - Required. The Unity Catalog-compatible naming for the gateway storage location. This is the destination to use for the data that is extracted by the gateway. Delta Live Tables system will automatically create the storage location under the catalog and schema.
   * `gateway_storage_schema` - Required, Immutable. The name of the schema for the gateway pipelines's storage location.
-
+* `event_log` - an optional block specifying a table where DLT Event Log will be stored.  Consists of the following fields:
+  * `name` - (Required) The table name the event log is published to in UC.
+  * `catalog` - (Optional, default to `catalog` defined on pipeline level) The UC catalog the event log is published under.
+  * `schema` - (Optional, default to `schema` defined on pipeline level) The UC schema the event log is published under.
 
 ### notification block
 

pipelines/resource_pipeline.go

@@ -213,21 +213,19 @@ func (Pipeline) CustomizeSchema(s *common.CustomizableSchema) *common.Customizab
 	s.SchemaPath("ingestion_definition", "ingestion_gateway_id").SetForceNew()
 
 	// Computed fields
-	s.SchemaPath("id").SetComputed()
 	s.SchemaPath("cluster", "node_type_id").SetComputed()
 	s.SchemaPath("cluster", "driver_node_type_id").SetComputed()
 	s.SchemaPath("cluster", "enable_local_disk_encryption").SetComputed()
-	s.SchemaPath("url").SetComputed()
-
-	s.SchemaPath("state").SetComputed()
-	s.SchemaPath("latest_updates").SetComputed()
-	s.SchemaPath("last_modified").SetComputed()
-	s.SchemaPath("health").SetComputed()
-	s.SchemaPath("cause").SetComputed()
-	s.SchemaPath("cluster_id").SetComputed()
-	s.SchemaPath("creator_user_name").SetComputed()
-	s.SchemaPath("run_as").SetComputed()
-	s.SchemaPath("run_as_user_name").SetReadOnly()
+
+	for _, field := range []string{"id", "state", "latest_updates", "last_modified",
+		"health", "cause", "cluster_id", "creator_user_name", "run_as", "url", "run_as_user_name"} {
+		s.SchemaPath(field).SetComputed()
+	}
+
+	// customize event_log
+	s.SchemaPath("event_log", "name").SetRequired()
+	s.SchemaPath("event_log", "catalog").SetComputed()
+	s.SchemaPath("event_log", "schema").SetComputed()
 
 	// SuppressDiff fields
 	s.SchemaPath("edition").SetSuppressDiff()