Backport of Net 6820 customize mesh gateway limits into release/1.18.x

[hc-github-team-consul-core]

Backport

This PR is auto-generated from #20945 to be assessed for backporting due to the inclusion of the label backport/1.18.

🚨

Warning automatic cherry-pick of commits failed. If the first commit failed,
you will see a blank no-op commit below. If at least one commit succeeded, you
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The person who merged in the original PR is:
@sarahalsmiller
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: unable to process merge commit: "250b5b29a2b7a320a5464981ae5abc51630701cc", automatic backport requires rebase workflow

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

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Description

Allow users of Mesh Gateway to add custom circuit breakers to the mesh gateway XDS config by using a ServiceDefaults object named MeshGateway

• We based this implementation on the first option described in this comment since we didn't want to blow out the scope of this story by adding a new config object, even though we believe that to be the better long term strategy. Configurable limits/circuit breakers on mesh-gateways #13589 (comment)

Testing & Reproduction steps

• Using a built image, tested creating a mesh gateway to make sure the snapshot was updated appropriately
• Added a new golden file test to cover adding XDS

Links

PR Checklist

• [ X ] updated test coverage
• external facing docs updated
• appropriate backport labels added
• not a security concern

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Overview of commits

• cf7ea96 - c1a0da9 - cd5b14e - f2d9989 - 4b6ceb3 - c2e0794 - 250b5b2 - 231cca8 - 50fbf6c - c715f3c - 1e123fc - 2260f8b - e286a72 - b4692c6 - 65262a2 - 69f5065

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

Auto approved Consul Bot automated PR

[david-yu]

@sarahalsmiller Gentle nudge t review and merge when ready