[Feature Suggestion] Multi-row delete function (w/working implementation)

Realized that deleting multiple rows one-by-one can take an extremely long time, especially when working with sheets with 1000+ rows, or have e.g. 500+ rows to delete.

I created a function to delete multiple rows by breaking list of row indexes into contiguous ranges and sending a single batchUpdate API call with multiple requests.

see delete_rows() function: https://github.com/eavalenzuela/gspread/blob/master/gspread/models.py

e.g.
[1,2,3,4,6,7,9,11,13,14,15]
becomes
[(1:4), (6:7), 9, 11, (13:15)]
i.e. 5 deleteDimension requests instead of 11, and all in 1 function call instead of doing a loop of delete_row(). It has **very** significantly reduced the time to remove large numbers of rows from sheets in my testing.

It does currently rely on the more_itertools package for the "consecutive_groups()" function, but that functionality could be added internally here if desired, to eliminate the dependency.

Start with gspread/models.py and the linked delete_rows() implementation. Review how consecutive row indexes are grouped and how one Google Sheets batchUpdate call can carry multiple deleteDimension requests; done means supporting the requested multi-row deletion without repeatedly calling delete_row().

Written by the indexing model from the issue text.