User feedback on Authentication docs

What does this MR do?

Addresses several comments from users on our existing documentation.

1. The info for for Reset 2FA on your account is not accurate as you have to login to submit a ticket. But you can't login if your 2fa is missing or not working.
1. I'm trying to find the instructions that used to be here on how to generate a token for an instance level service account for self-managed.  It appears to no longer be documented, and I need to rotate the expired token.
1. How do you delete the old / mistake tokens? The page only mentions how to revoke. However, revoking keeps the token. I want to eliminate / remove it and I can't seem to find the configuration for this.
1. which URL for changing my forgotten password ?

Related issues

https://gitlab.com/gitlab-org/gitlab/-/issues/564995

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