Add a limit on channel group creation

Same as exists for channels

This is a backport of the fix in ag/16659457, including the adjustment from ag/20920023 (changed the max value from 50000 to 6000).

Test: PreferencesHelperTest
Bug: 210114537
Bug: 261723753
Change-Id: Ic27efba4c54e22eebca16fc948879e652df4467b
(cherry picked from commit 37b35498 & I3f3a99765c161369e1b026686a0e5f0c83ed839e)
Merged-In: I3f3a99765c161369e1b026686a0e5f0c83ed839e
Merged-In: Ic27efba4c54e22eebca16fc948879e652df4467b