Improve Slack Integration

[jan-auer]

Initially, this bot was planned to work only with GitHub and integrate optionally with Slack. However, this introduces some problems:

• Not every user has a public email configured in their account. In that case, the bot is not able to reach them at all
• There is no way to obtain the email configured for the GitHub organization (e.g. work email). However, people don't like to receive those notifications on their personal email.
• The GitHub API does not offer a reliable way to determine a user's time zone
• Many people prefer communication via Slack over email

Instead, the bot could focus on Slack for user management:

• Users are read from the Slack team instead of GitHub
• The email used in the Slack team is more likely to be related to the work in the organization
• Once a new user gets added, the bot can immediately message them. This also increases the level of engagement
• Users still have to link to GitHub first. The GitHub team check can still be performed, then
• As far as I know, the Slack API also exposes users' time zones

[jan-auer]

@HazAT any comments on this?

[HazAT]

This is not a bad idea but it would need a real Slack App afaik.
Currently, the Slack integration is a simple bot and I think you are not able to fetch all users, a user has to first write the bot in order for the bot to retrieve the user.