feat: add flagd provider

[tcarrio]

This PR

This PR was started using commits from python-sdk from @agardnerIT. See the original PR for more info. It has since been refactored to the structure of python-sdk-contrib and into multiple Python modules to further separate concerns. Certain files have been incorporated from python-sdk (mainline and PRs in reviews).

Related Issues

Provides the initial flagd provider.

Notes

• Incorporates the pyproject.toml structure for publishing
• Incorporates the Makefile in open-feature/python-sdk#31
• Incorporates the CONTRIBUTING.md from open-feature/python-sdk#31 / open-feature/js-sdk

Follow-up Tasks

Clean up, linting, masking internal methods, etc.

How to test

Initial unit tests included.

[codecov-commenter]

Codecov Report

Merging #3 (b3defb0) into main (eadcb28) will increase coverage by 72.00%.
The diff coverage is 72.00%.

@@            Coverage Diff            @@
##           main       #3       +/-   ##
=========================================
+ Coverage      0   72.00%   +72.00%     
=========================================
  Files         0        7        +7     
  Lines         0      100      +100     
=========================================
+ Hits          0       72       +72     
- Misses        0       28       +28     

Flag	Coverage Δ
unittests	72.00% <72.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
open_feature_contrib/providers/flagd/provider.py	60.00% <60.00%> (ø)
...ure_contrib/providers/flagd/web_api_url_factory.py	70.37% <70.37%> (ø)
...b/providers/flagd/evaluation_context_serializer.py	71.42% <71.42%> (ø)
open_feature_contrib/providers/flagd/__init__.py	100.00% <100.00%> (ø)
open_feature_contrib/providers/flagd/defaults.py	100.00% <100.00%> (ø)
open_feature_contrib/providers/flagd/flag_type.py	100.00% <100.00%> (ø)
tests/providers/conftest.py	100.00% <100.00%> (ø)

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[jamescarr]

@tcarrio what else does this PR need to merge? Happy to pitch in and assist!

[tcarrio]

@jamescarr I wanted to do a review of the CONTRIBUTING.md file to make sure all references were updated. Outside of that this should be good to merge as the initial alpha of the Flagd provider (utilizing the gRPC Web endpoints of Flagd).

I noticed you've introduced a new Makefile as well in #9. That can likely expand on the one in here, which already targets requirements-dev for local dev setup. Other than that though that one provides a better DX like default help output, so thanks for that 😉

[federicobond]

• Rebased on top of latest main with permission from @tcarrio
• Splitted off the CONTRIBUTING.md docs change to docs: add CONTRIBUTING.md from python-sdk #10

[toddbaert]

I'm approving this in concept, but I will differ to @federicobond for the finer details.

[federicobond]

I think this is good for a first version. We should probably replace it with a gRPC transport version down the road.