Backport of [API Gateway] Add acceptance test for cluster peering into release/1.2.x

[hc-github-team-consul-core]

Backport

This PR is auto-generated from #2306 to be assessed for backporting due to the inclusion of the label backport/1.2.x.

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The person who merged in the original PR is:
@andrewstucki
This person should manually cherry-pick the original PR into a new backport PR,
and close this one when the manual backport PR is merged in.

merge conflict error: POST https://api.github.com/repos/hashicorp/consul-k8s/merges: 409 Merge conflict []

The below text is copied from the body of the original PR.

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Changes proposed in this PR:
This adds an acceptance test for cluster peering with API gateways. It depends on this fix hashicorp/consul#17609 landing in Consul with how we construct synthesized discovery chains, so it will need to land after that gets merged and a docker image is cut.

How I've tested this PR:
Ran acceptance test with fixed version of Consul and it passes.

Checklist:

• Tests added
• CHANGELOG entry added

  HashiCorp engineers only, community PRs should not add a changelog entry.
  Entries should use present tense (e.g. Add support for...)

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Overview of commits

• 0db1259 - d4cdb45 - fdeccab - 030c563 - 6210dff - 4476e8e - 1dbc569 - bb7ed17 - 52bd813