chore: Prettify "Time's up" Slack message

[Dschoordsch]

Format the "Time's up" message similar to the rest of the messages. MSTeams seems to have a nicely formatted message already.

Demo

Before:

Now:

Testing scenarios

For ease of testing I replaced

parabol/packages/server/graphql/public/mutations/startCheckIn.ts

Line 113 in 3512182

IntegrationNotifier.startMeeting(dataLoader, meetingId, teamId)

with

  IntegrationNotifier.endTimeLimit(dataLoader, meetingId, teamId)

and just started a check-in

• check Slack
• check Mattermost

Final checklist

• I checked the code review guidelines
• I have added Metrics Representative as reviewer(s) if my PR invovles metrics/data/analytics related changes
• I have performed a self-review of my code, the same way I'd do it for any other team member
• I have tested all cases I listed in the testing scenarios and I haven't found any issues or regressions
• Whenever I took a non-obvious choice I added a comment explaining why I did it this way
• I added the label Skip Maintainer Review Indicating the PR only requires reviewer review and can be merged right after it's approved if the PR introduces only minor changes, does not contain any architectural changes or does not introduce any new patterns and I think one review is sufficient'
• PR title is human readable and could be used in changelog