Follow-up from "Documentation revision: PAT notification emails"

The following discussion from !30974 (merged) should be addressed:

• @mjang1 started a discussion:
• Add doc related to !19296 (merged), possibly in https://docs.gitlab.com/ee/user/profile/personal_access_tokens.html or https://docs.gitlab.com/ee/user/profile/notifications.html
• Resolve sidekiq exceptions noted by @bprescott_ in !30974 (comment 336090901)