[Draft] feat: Initial codecov endpoint for fetching test results

[ajay-sentry]

This PR is currently a draft.

This PR aims to create our first codecov (mocked) endpoint for test results, a "get" endpoint that calls the codecov client with different graphql queries depending on the request url.

Legal Boilerplate

Look, I get it. The entity doing business as "Sentry" was incorporated in the State of Delaware in 2015 as Functional Software, Inc. and is gonna need some rights from me in order to utilize my contributions in this here PR. So here's the deal: I retain all rights, title and interest in and to my contributions, and by keeping this boilerplate intact I confirm that Sentry can use, modify, copy, and redistribute my contributions, under Sentry's choice of terms.

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
25958	1	25957	207

View the top 1 failed test(s) by shortest run time

tests.sentry.api.test_api_owners.APIOwnersTestCase::test_api_owner_owns_api

Stack Traces | 0.044s run time

#x1B[1m#x1B[.../sentry/api/test_api_owners.py#x1B[0m:22: in test_api_owner_owns_api
    assert owner.value in self.teams
#x1B[1m#x1B[31mE   AssertionError: assert 'codecov' in {'alerts-create-issues', 'alerts-notifications', 'core-product-foundations', 'crons', 'dashboards', 'data', ...}#x1B[0m
#x1B[1m#x1B[31mE    +  where 'codecov' = <ApiOwner.CODECOV: 'codecov'>.value#x1B[0m
#x1B[1m#x1B[31mE    +  and   {'alerts-create-issues', 'alerts-notifications', 'core-product-foundations', 'crons', 'dashboards', 'data', ...} = <tests.sentry.api.test_api_owners.APIOwnersTestCase testMethod=test_api_owner_owns_api>.teams#x1B[0m

To view more test analytics, go to the Test Analytics Dashboard
_{📋 Got 3 mins? Take this short survey to help us improve Test Analytics.}