feat(labels): Add support for retrieve labels using their external ids

[sagar-thalwar]

Description

Add support for retrieving labels using their external ids

Checklist:

• [x] Tests added/updated.
• [x] Documentation updated. Documentation is generated from docstrings - these must be updated according to your change. If a new method has been added it should be referenced in cognite.rst in order to generate docs based on its docstring.
• [x] Changelog updated in CHANGELOG.md.
• [x] Version bumped. If triggering a new release is desired, bump the version number in _version.py and pyproject.toml per semantic versioning.

[codecov[bot]]

Codecov Report

Merging #1704 (b84fe52) into master (e6c7f1c) will decrease coverage by 0.04%. The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1704      +/-   ##
==========================================
- Coverage   92.73%   92.70%   -0.04%     
==========================================
  Files         121      121              
  Lines       17055    17062       +7     
==========================================
+ Hits        15816    15817       +1     
- Misses       1239     1245       +6     

Files	Coverage Δ
cognite/client/_api/labels.py	97.56% <100.00%> (+0.50%)	:arrow_up:
cognite/client/_version.py	100.00% <100.00%> (ø)

... and 3 files with indirect coverage changes

[erlendvollset]

Add test cases for retrieving unknown ids and it's good to go!

[doctrino]

Did not notice this one but I fixed this in #1795

Suggest closing this PR.