[Internal] Fixed documentation for budget_policy until it's fixed in proto (#4708)

## Changes
<!-- Summary of your changes that are easy to understand -->
This needs to be fixed in proto as it's autogenerated, fixing it here
for time being as we have a ticket to follow up with cluster team.

## Tests
<!-- 
How is this tested? Please see the checklist below and also describe any
other relevant tests
-->
N/A
- [ ] `make test` run locally
- [ ] relevant change in `docs/` folder
- [ ] covered with integration tests in `internal/acceptance`
- [ ] using Go SDK
- [ ] using TF Plugin Framework

Author: tanmay-db

NEXT_CHANGELOG.md

@@ -11,3 +11,4 @@
 ### Exporter
 
 ### Internal Changes
+* Fixed documentation for budget_policy until it's fixed in proto [#4708](https://github.com/databricks/terraform-provider-databricks/pull/4708)