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
Closes #2704

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 94.49686% with 35 lines in your changes missing coverage. Please review.

Project coverage is 86.69%. Comparing base (6337c97) to head (9c180d5).
Report is 186 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%   86.69%   -3.06%     
===================================================================
  Files                                  109      125      +16     
  Lines                                11150    14447    +3297     
  Branches                                50       62      +12     
===================================================================
+ Hits                                 10007    12525    +2518     
- Misses                                1083     1784     +701     
- Partials                                60      138      +78     

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[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.

[salonichf5]

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.

Thank you for helping me.

[bjee19]

Great job on the PR, just some small things.

[bjee19]

LGMT, great job! 🚀

[ciarams87]

🚀 🚀 🚀