Update Databricks Section of grants.md (#4053)

Add bullet point for Databricks specific grants that aren't supported by
dbt grants

## What are you changing in this pull request and why?
<!---
Describe your changes and why you're making them. If linked to an open
issue or a pull request on dbt Core, then link to them here! 

To learn more about the writing conventions used in the dbt Labs docs,
see the [Content style
guide](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/content-style-guide.md).
-->
Changing the grants docs for Databricks. Currently rights like
`READ_METADATA` and `USAGE` are not supported by dbt `grant` and need to
use post-hooks for this

## Checklist
- [ ✅ ] Review the [Content style
guide](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/content-style-guide.md)
and [About
versioning](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/single-sourcing-content.md#adding-a-new-version)
so my content adheres to these guidelines.

website/docs/reference/resource-configs/grants.md

@@ -243,6 +243,7 @@ models:
 - Databricks automatically enables `grants` on SQL endpoints. For interactive clusters, admins should enable grant functionality using these two setup steps in the Databricks documentation:
   - [Enable table access control for your workspace](https://docs.databricks.com/administration-guide/access-control/table-acl.html)
   - [Enable table access control for a cluster](https://docs.databricks.com/security/access-control/table-acls/table-acl.html)
+- In order to grant `READ_METADATA` or `USAGE`, use [post-hooks](https://docs.getdbt.com/reference/resource-configs/pre-hook-post-hook)
 
 </div>