[v15] Refactor the Database Object Permissions guide (#42361)

* Refactor the Database Object Permissions guide

Closes #41917

Merge the Database Object Permissions guide into the Database Access
RBAC guide for greater discoverability and a clearer division of labor
between the two guides.

This change also includes the following edits to make the refactor
cleaner, since we can include each troubleshooting step as a separate H3
in the dateabase object permissions H2:

- Remove an unnecessary troubleshooting step: One step indicates that
  import rules are validated, which is unnecessary to document, since
  validation errors are self explanatory.
- Instead of mentioning the admin user as a troubleshooting step, add a
  separate H3 for the admin user and describe the `admin_user` field,
  which was not mentioned in the original database object permissions
  guide.

* Respond to Tener feedback

- Clarify the placing of the `admin_user` field

* Restore intro section

Per Tener and r0mant feedback, integrate the introduction from the
Database Access Controls page into the newly merged RBAC guide. Frame
Database Access Controls as encompassing both databases and database
objects.

* Respond to r0mant feedback

* Fix spelling

* Fix linter issues

docs/config.json

@@ -1554,10 +1554,6 @@
             {
               "title": "PostgreSQL",
               "slug": "/database-access/auto-user-provisioning/postgres/"
-            },
-            {
-              "title": "Database Access Controls",
-              "slug": "/database-access/auto-user-provisioning/database-access-controls/"
             }
           ]
         },

docs/pages/database-access/auto-user-provisioning.mdx

@@ -5,8 +5,6 @@ description: Configure automatic user provisioning for databases.
 
 (!docs/pages/includes/database-access/auto-user-provisioning/intro.mdx!)
 
-Automatically created users will either receive a predefined set of roles, or can be granted permissions to specific database objects based on their required level of access using [Database Access Controls](./auto-user-provisioning/database-access-controls.mdx) feature.
-
 Currently, automatic user provisioning is supported for the following databases:
 - [PostgreSQL databases (self-hosted and AWS RDS)](./auto-user-provisioning/postgres.mdx)
 - [MySQL databases (self-hosted and AWS RDS)](./auto-user-provisioning/mysql.mdx)

docs/pages/database-access/auto-user-provisioning/postgres.mdx

@@ -61,7 +61,7 @@ to ensure that your configuration is correct.
 </Tabs>
 
 <Admonition type="note" title="Database Access Controls for `teleport-admin`">
-When [Database Access Controls](./database-access-controls.mdx) feature is in use, the `teleport-admin` should have permissions to relevant database objects. For example:
+When [Database Access Controls](../rbac.mdx) feature is in use, the `teleport-admin` should have permissions to relevant database objects. For example:
 
 ```sql
 GRANT ALL PRIVILEGES ON ALL TABLES IN SCHEMA schema1, schema2, schema3 TO "teleport-admin";
@@ -148,7 +148,7 @@ version: v7
 
 You can define your own labels for database objects, applying them based on customizable import rules. These custom labels, such as `owner` or `environment`, can then be utilized when granting permissions.
 
-For additional information, refer to the [Database Access Controls](./database-access-controls.mdx) page.
+For additional information, refer to the [Database Access Controls](../rbac.mdx) page.
 
 </TabItem>
 </Tabs>