DEPR: rename BQ to BQE for offsets
xref #55553, #55496, #52064

Deprecated the alias denoting business quarter end frequency  `'BQ'` for offsets in favour of `'BQE'`. 
Renamed strings 'BQ-DEC', 'BQ-JAN', etc. denoting business quarterly frequencies with various fiscal quarter ends to 'BQE-DEC', 'BQE-JAN', etc.
Thank you for reviewing this PR. I will add the note to whatsnew and will remove the entries "BM", "CBM" in the next PR.
