DOC-13651: Incorrect role names in GRANT and REVOKE

[simon-dew]

Docs issue: DOC-13651

Making the changes on 7.6 first so we don't get in the way of the 8.0 release 😄

Preview URL:

• GRANT
• REVOKE

You will need the Docs Team credentials on Confluence.

[GauravJayaraj]

LGTM!

[rakhi-prathap]

Looks good, just two tiny comments.

Also, if you're planning to port this to 8.0 -

• Some of these changes are already in 8.0, though not all. See PR 392.
• Looking at PR 392 now, I notice a few errors in it. I believe the part about keyspace needing to be fully qualified is wrong. I can’t recall why that change was made.
  I’ll create a fast-follow item to review and fix it.