sql: support ALTER ROLE ... RENAME TO ...

[solongordon]

CockroachDB currently does not support renaming an existing role directly. In order to do so, you need to create a new role with the same privileges and then drop the old one.

Supporting rename is not trivial as it stands because all privileges are keyed off of the role name. This is made more difficult by the fact that privileges are stored directly on descriptors, not in system tables.

Jira issue: CRDB-4084

Epic CRDB-25679

[solongordon]

@awoods187 pointed out we could also consider implementing this by having a job which walked through the steps a user would do manually: creating the new role, granting the same privileges, assigning other roles to it, etc. That would still take some care to get right but would not require a larger overhaul to how we store privileges.

[RichardJCai]

Depends on the work here:
#78963

[RichardJCai]

Let's wait for 23.1 to make thing's simpler - once the role_id work is in and has baked for a version such that we're guaranteed to have role ids.

[AndrewSouthpaw]

Just ran into this limitation. The workaround isn't so bad, but it'd be nice to see this in CRDB at some point!