Add documentation for missing service_principal_client_id attribute (#5134)

## Changes
<!-- Summary of your changes that are easy to understand -->
Added documentation for missing attribute [databricks_app
attribute](#5128).

Resolves #5128


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

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

Author: excavator-matt

NEXT_CHANGELOG.md

@@ -14,6 +14,7 @@
 
 ### Documentation
 
+* Add documentation on the `service_principal_client_id` attribute of `databricks_app` and related [#5134](https://github.com/databricks/terraform-provider-databricks/pull/5134)
 ### Exporter
 
 ### Internal Changes

docs/data-sources/app.md

@@ -43,6 +43,7 @@ In addition to all arguments above, the following attributes are exported:
   * `creator` - The email of the user that created the app.
   * `update_time` - The update time of the app.
   * `updater` - The email of the user that last updated the app.
+  * `service_principal_client_id` - client_id (application_id) of the app service principal
   * `service_principal_id` - id of the app service principal
   * `service_principal_name` - name of the app service principal
   * `default_source_code_path` - The default workspace file system path of the source code from which app deployment are created. This field tracks the workspace source code path of the last active deployment.

docs/data-sources/apps.md

@@ -35,6 +35,7 @@ The following attributes are exported:
   * `creator` - The email of the user that created the app.
   * `update_time` - The update time of the app.
   * `updater` - The email of the user that last updated the app.
+  * `service_principal_client_id` - client_id (application_id) of the app service principal
   * `service_principal_id` - id of the app service principal
   * `service_principal_name` - name of the app service principal
   * `default_source_code_path` - The default workspace file system path of the source code from which app deployment are created. This field tracks the workspace source code path of the last active deployment.

docs/resources/app.md

@@ -99,6 +99,7 @@ In addition to all arguments above, the following attributes are exported:
 * `creator` - The email of the user that created the app.
 * `update_time` - The update time of the app.
 * `updater` - The email of the user that last updated the app.
+* `service_principal_client_id` - client_id (application_id) of the app service principal
 * `service_principal_id` - id of the app service principal
 * `service_principal_name` - name of the app service principal
 * `default_source_code_path` - The default workspace file system path of the source code from which app deployment are created. This field tracks the workspace source code path of the last active deployment.