…logic

Refactor the group cancellation process by moving the code from main()
into new functions, similar to the existing jobs cancellation functions.

Added `cancel_group` function along with its helper functions.

Notable change:

- Removed constraints from the old code, making it no longer mandatory
  for the group to have `groups_status OK`, or pending/running jobs.

This allows cancellations of both inactive and previously cancelled
groups.

These changes enable more flexible group management and simplify the
cancellation logic.

Note: The old code will be removed in the next commit for cleaner diffs
and improved clarity.

Use cancel_group() and remove old code.