Add support for multiple gateways

[salonichf5]

Proposed changes

Write a clear and concise description that helps reviewers understand the purpose and impact of your changes. Use the
following format:

Problem: Users want to be able to configure multiple gateways

Solution: Allows users to configure multiple gateways

Testing:

1. Added unit tests and fixed functional tests

Manual testing: tracking it here

Closes #3219
Closes #3213
Closes #1443

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Release notes

If this PR introduces a change that affects users and needs to be mentioned in the release notes,
please add a brief note that summarizes the change.

Add support for multiple gateways

[codecov]

Codecov Report

Attention: Patch coverage is 94.44444% with 35 lines in your changes missing coverage. Please review.

Project coverage is 86.72%. Comparing base (6337c97) to head (8713cd6).
Report is 185 commits behind head on change/control-data-plane-split.

Files with missing lines	Patch %	Lines
internal/mode/static/manager.go	6.66%	14 Missing ⚠️
internal/mode/static/handler.go	88.70%	4 Missing and 3 partials ⚠️
cmd/gateway/commands.go	14.28%	6 Missing ⚠️
...ernal/mode/static/state/dataplane/configuration.go	96.87%	2 Missing and 1 partial ⚠️
...nal/mode/static/nginx/config/policies/validator.go	77.77%	1 Missing and 1 partial ⚠️
internal/mode/static/state/graph/route_common.go	98.24%	1 Missing and 1 partial ⚠️
...rnal/mode/static/state/graph/backend_tls_policy.go	95.83%	1 Missing ⚠️

Additional details and impacted files

@@                         Coverage Diff                         @@
##           change/control-data-plane-split    #3275      +/-   ##
===================================================================
- Coverage                            89.74%   86.72%   -3.02%     
===================================================================
  Files                                  109      125      +16     
  Lines                                11150    14445    +3295     
  Branches                                50       62      +12     
===================================================================
+ Hits                                 10007    12528    +2521     
- Misses                                1083     1780     +697     
- Partials                                60      137      +77     

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[sjberman]

Why did this change not affect the outcome of the test?

[salonichf5]

I have no idea how this test was passing before, this is a valid case where type is invalid, the normal case targetRef kind was secret which was the allowed type for cert ref kind.

[sjberman]

Do we have a bug? Could be worth an investigation (out of scope for this, but could make a note of it to revisit after this is done).

[salonichf5]

good idea, let me make a note of it!

[sjberman]

Is this test case really needed? I know you're probably just trying to get coverage on the panic line, but is it even possible for us to call it like this?

[salonichf5]

Yes, it is possible to call it like this. This was just for coverage and also for the fact that we do have events with no gateways to update so wanted to be cautious

[sjberman]

LGTM, nice work.

I think once we get conformance tests working and we can run our full suite of all tests, we can get a better feeling of any issues that may have arisen.