feat(flags): add Unleash feature flagging integration

[aliu39]

Adds an integration for tracking flag evaluations from Unleash customers.

Implementation
Unleash has no native support for evaluation hooks/listeners, unless the user opts in for each flag. Therefore we decided to patch the is_enabled and get_variant methods on the UnleashClient class. The methods are wrapped and the only side effect is writing to Sentry scope, so users shouldn't see any change in behavior.

We patch one UnleashClient instance instead of the whole class. The reasons for this are described in

• ref(flags): allow OpenFeature integration to track a single client #3895

It's also safer to not modify the unleash import.

References

• https://develop.sentry.dev/sdk/expected-features/#feature-flags
• https://docs.getunleash.io/reference/sdks/python for methods we're patching/wrapping

Documentation PR

• feat(flags): document python UnleashIntegration sentry-docs#12216

[codecov]

Codecov Report

Attention: Patch coverage is 93.75000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 79.87%. Comparing base (7f73c9e) to head (95c72e9).
Report is 3 commits behind head on master.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
sentry_sdk/integrations/unleash.py	93.75%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3888      +/-   ##
==========================================
+ Coverage   79.83%   79.87%   +0.03%     
==========================================
  Files         139      140       +1     
  Lines       15419    15451      +32     
  Branches     2623     2624       +1     
==========================================
+ Hits        12310    12341      +31     
- Misses       2235     2237       +2     
+ Partials      874      873       -1     

Files with missing lines	Coverage Δ
sentry_sdk/integrations/unleash.py	93.75% <93.75%> (ø)

... and 1 file with indirect coverage changes

[antonpirker]

Hey @aliu39 ! Thanks for the integration. This will be reviewed after the holiday season.

[aliu39]

Todo:

• verify w manual test
• threading and asyncio tests
• determine if variant payload should factor into tracking (no, track every feature)
• docs w/ sample verification code

[cmanallen]

Mutating class attributes in the __init__ method violates encapsulation. There are a whole category of problems which come from this. I've removed it and replaced with by mutating the UnleashClient class directly. I noticed in the tests you were testing for isolation between instances. While that's interesting it isn't the goal. We want to inject ourselves into every instance or none. This follows the behavior of our other integrations.

Also I've reverted the changes in conftest.py. There was nothing wrong with them. They are just out of scope for this unit of work. Feel free to do those in a follow up PR.

[cmanallen]

Blocking this. We're going to talk about how we handle this going forward and may close this.

[cmanallen]

Okay we're all good. We're going to keep this setup.

[antonpirker]

Looks good to me.
Nice integrations, and GREAT test suite! Thanks for that!