docs: support for Google Cloud Load balancers

[kostis-codefresh]

Closes #1079

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this is a chore.
• The title of the PR is (a) conventional with a list of types and scopes found here, (b) states what changed, and (c) suffixes the related issues number. E.g. "fix(controller): Updates such and such. Fixes #1234".
• I've signed my commits with DCO
• I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• My builds are green. Try syncing with master if they are not.
• My organization is added to USERS.md.

[github-actions]

Go Published Test Results

1 983 tests   1 983 ✔️  2m 36s ⏱️
   118 suites         0 💤
       1 files           0 ❌

Results for commit d8968b2.

♻️ This comment has been updated with latest results.

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (6ac1533) 81.68% compared to head (d514eee) 81.68%.

❗ Current head d514eee differs from pull request most recent head d8968b2. Consider uploading reports for the commit d8968b2 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2803   +/-   ##
=======================================
  Coverage   81.68%   81.68%           
=======================================
  Files         133      133           
  Lines       20178    20178           
=======================================
  Hits        16483    16483           
  Misses       2843     2843           
  Partials      852      852           

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.

[github-actions]

E2E Tests Published Test Results

    4 files      4 suites   3h 24m 52s ⏱️
  96 tests   81 ✔️   5 💤 10 ❌
396 runs  365 ✔️ 20 💤 11 ❌

For more details on these failures, see this check.

Results for commit d8968b2.

♻️ This comment has been updated with latest results.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[zachaller]

Can we add the gateway-api to the list of plugins here https://argo-rollouts.readthedocs.io/en/stable/features/traffic-management/plugins/

[kostis-codefresh]

@zachaller this was already done by @todaywasawesome last week by this PR #2787

It is live in the "latest" docs https://argo-rollouts.readthedocs.io/en/latest/features/traffic-management/plugins/