Backport of [API Gateway] WAN Federation test and fixes into release/1.2.x

[hc-github-team-consul-core]

Backport

This PR is auto-generated from #2295 to be assessed for backporting due to the inclusion of the label backport/1.2.x.

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

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Changes proposed in this PR:
This adds a WAN federation acceptance test for API Gateways. A few fixes went into it:

1. We were disallowing ServiceResolver cross-DC redirects unless someone was explicitly in the default partition, but were only checking for "default" when an empty string means the same thing
2. We needed to normalize the auth method name that we use for our deployments so that we use the DC-local one that we attach our binding rules to.
3. Due to the way we watch and GC config entries, we needed to pass some additional metadata to ignore anything coming from a sync to a federated DC -- basically we were removing config entries if we didn't have the corresponding Kubernetes object backing them in our DC, when we shouldn't touch them because a corresponding Kubernetes object exists for them in another DC.

How I've tested this PR:
I tested this by running this locally on Kind with MetalLB installed so that the mesh gateways could find each other over WAN, but this doesn't typically work in a Kind setup, as the other acceptance test mentions, so it will be disabled for typical CI runs.

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

• 3f1c9e0 - c56ac76