chore(ci): extract reusable workflows

[czeslavo]

What this PR does / why we need it:

Extracts parts of the existing workflows that are repeated across some of them (e.g. _test_reports.yaml), or encapsulates more complex parts into their own workflow so that they're easier to reason about in isolation (e.g. _integration_tests.yaml).

All of the workflows that are extracted as reusable are named following the _name.yaml pattern to make them easily distinguishable.

Runs of the affected top-level workflows:

• e2e (targeted): https://github.com/Kong/kubernetes-ingress-controller/actions/runs/4430100543
• e2e (nightly): https://github.com/Kong/kubernetes-ingress-controller/actions/runs/4430187170 (failed on codecov, but fixed that in the code by disabling codecov report in this workflow)
• nightly: https://github.com/Kong/kubernetes-ingress-controller/actions/runs/4430091411 (failed due to missing permissions for this branch)
• PR validation: https://github.com/Kong/kubernetes-ingress-controller/actions/runs/4430191048

Which issue this PR fixes:

Part of #3349.
It also enables E2E tests in the PR workflow as a part of #3725.

Special notes for your reviewer:

GH's docs on the reusable workflows: https://docs.github.com/en/actions/using-workflows/reusing-workflows

If we decide to accept this PR, we'll need someone with wider permissions set to change the required PR status checks, as the old ones are remaining stuck with Waiting for status to be reported.

[pmalek]

Nice work 👍

Couple of open ended questions for consideration

[czeslavo]

@rainest @pmalek I hope I addressed all the comments, PTAL again. 🙏

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -16.7 ⚠️

Comparison is base (50a4c3f) 73.6% compared to head (0e9f24c) 56.9%.

Additional details and impacted files

@@           Coverage Diff            @@
##            main   #3724      +/-   ##
========================================
- Coverage   73.6%   56.9%   -16.7%     
========================================
  Files        133     133              
  Lines      15828   15828              
========================================
- Hits       11651    9017    -2634     
- Misses      3418    6191    +2773     
+ Partials     759     620     -139     

see 50 files with indirect coverage changes

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[pmalek]

🚢 🤞

[czeslavo]

@pmalek I pushed one more commit adding a passed job that we will be able to use as the only required check in the repository's branch protection rules. As we have many matrix-generated jobs it's the only way to gather all the results into one and be ready for changes in the matrices in the future.

[pmalek]

@pmalek I pushed one more commit adding a passed job that we will be able to use as the only required check in the repository's branch protection rules. As we have many matrix-generated jobs it's the only way to gather all the results into one and be ready for changes in the matrices in the future.

This is a very good idea but hard to get right ;) We have to take into account PRs from forks (which is OK to not cover here because we have an issue tracking this) and also cancelled jobs. But let's take an iterative approach on this. 🙃

[rainest]

Override merge since the checks pass, but Github won't let me say that they're the checks that should pass until they're merged 🐔 🥚 ♾️