Backport of [OSS] Improve Gateway Test Coverage of Catalog Health into release/1.15.x

[hc-github-team-consul-core]

Backport

This PR is auto-generated from #18011 to be assessed for backporting due to the inclusion of the label backport/1.15.

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The person who merged in the original PR is:
@DanStough
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/merges: 409 Merge conflict []

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

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Description

Two parts to this PR:

1. I wanted to increase test coverage for gateways because I had to revert a recent change caused by the health check failing on startup.
2. In adding this test coverage, I discovered that the default check registered to API gateways with consul connect envoy is invalid.

Testing & Reproduction steps

1. Run the integration tests.

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Overview of commits

• 954bd6a - 85c32d8 - 7ea3d62 - 127ae69 - e04099b

[github-team-consul-core-pr-approver]

Auto approved Consul Bot automated PR