Expose keep_excessive_supervision parameter

[nshmyrev]

Currently when supervision is slightly longer than recording user gets very confusing message about multiple channels:

Trimmed cut has supervisions with different channels. Either set keep_all_channels=True to keep original channels or keep_overlapping=False to retain only 1 supervision per trimmed cut.

This is because keep_overlapping is False and thus we filter out those bad supervisions. And keep_overalapping actually has nothing about the problem of wrong supervision times. One better expose keep_excessive_supervision parameter to method and provide more straightforward assert message.

[desh2608]

I think it may be better to first use fix_manifests() from lhotse/qa.py, instead of this. Then the longer supervisions will be trimmed to the recording length.

[pzelasko]

I agree with Desh, I'd rather not add support for supervision.duration > recording.duration, as it can be easily auto-fixed. We could emit a cleaner error message though.