feat(standups): Recurrence - `stopRecurrence` mutation

[BartoszJarocki]

Description

Fixes #6918

Demo

Testing scenarios

• [ ] Create a standup meeting and...
  • Set up recurrence using menu in the top right corner
  • Stop the recurrence using menu in the top right corner
  • Check rethinkdb if given meeting have scheduledEndTime set to null
  • Check postgres if related meeting series have cancelledAt set to a proper date

Final checklist

• [x] I checked the code review guidelines
• [x] I have added Metrics Representative as reviewer(s) if my PR invovles metrics/data/analytics related changes
• [x] I have performed a self-review of my code, the same way I'd do it for any other team member
• [x] I have tested all cases I listed in the testing scenarios and I haven't found any issues or regressions
• [x] Whenever I took a non-obvious choice I added a comment explaining why I did it this way
• [x] I added the label One Review Required 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'
• [x] PR title is human readable and could be used in changelog

[BartoszJarocki]

@mattkrick would you mind taking a look? thank you!