added files.get_tags function

[bigcat88]

Fixes #259

    nc = nc_py_api.Nextcloud(nc_auth_user="admin", nc_auth_pass="admin", nextcloud_url="http://stable29.local")
    some_file = nc.files.by_path("New folderz/1.txt")
    some_file_tags = nc.files.get_tags(some_file)
    print(some_file_tags)

Output:

[<SystemTag id=1, name=first>, <SystemTag id=2, name=second>]

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.75%. Comparing base (5d41bf9) to head (9f70fc2).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #260      +/-   ##
==========================================
+ Coverage   95.72%   95.75%   +0.03%     
==========================================
  Files          45       46       +1     
  Lines        5261     5301      +40     
==========================================
+ Hits         5036     5076      +40     
  Misses        225      225              

Files	Coverage Δ
nc_py_api/__init__.py	100.00% <100.00%> (ø)
nc_py_api/files/_files.py	98.59% <100.00%> (+0.06%)	⬆️
nc_py_api/files/files.py	100.00% <100.00%> (ø)
nc_py_api/files/files_async.py	100.00% <100.00%> (ø)
nc_py_api/nextcloud.py	98.00% <100.00%> (+<0.01%)	⬆️