support local_infile_dir option

[RasmusKard]

Adds support for MYSQL_OPT_LOAD_DATA_LOCAL_DIR in mysql_options() as the kwarg local_infile_dir. A bit safer alternative than local_infile for MySQL versions >= 8.0.21.

(P.S. I'm a bit out of my depth with this PR but tried my best following the example of a previous PR with a similar addition, if there is anything that needs changing I'm happy to do it.)

Thank you for reviewing!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.84%. Comparing base (e2a908b) to head (e1e1853).
Report is 28 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #755      +/-   ##
==========================================
- Coverage   88.86%   88.84%   -0.02%     
==========================================
  Files           7        7              
  Lines         548      556       +8     
==========================================
+ Hits          487      494       +7     
- Misses         61       62       +1     

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