Automate Slack usernames based on group

Could be cool to have [RTP] [Financial] [Drink Admin] and do it all in an automated way

Start by tracing the Flask endpoint and its LDAP, GitHub-login, and Slack-login account-linking flows. Define how group memberships map to usernames, including groups such as RTP, Financial, and Drink Admin, and document the expected result before implementing and testing the automation.

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