Is your feature request related to a problem? Please describe.
Part of: #89429

As part of our effort to migrate to a multi-tenant architecture, we need to ensure our existing databases endpoint is tenant-scoped.

Fortunately, the existing endpoint is implemented using SQL, meaning the remaining work to be done is implementing the same endpoint for our tenantAdminServer, where we can use the same databasesHelper function (alternatively, we can use the sql-over-http endpoint: #79663, which will become tenant-scoped with the completion of #80789).

Reference PR adding the endpoint to the tenantAdminServer: #84620, making the Jobs and Job endpoints tenant-scoped

Jira issue: CRDB-20659