Backport of Separate port and socket path validation for local agent into release/1.13.x

[hc-github-team-consul-core]

Backport

This PR is auto-generated from #13906 to be assessed for backporting due to the inclusion of the label backport/1.13.

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

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Description

PR #12881 Introduced a requirement for either port or socket path to be provided in all requests. Due to a race in automatic port assignment within the agent, automatic assignment needs to be moved from the request-building stage to the locked registration stage post-validation. One solution (this PR) is to exempt the port requirement from request validation when the request is coming from an agent that is trying to do auto-assignment.

Testing & Reproduction steps

• Manually registering a service from the agent still works with and without a port specified.
• Existing unit tests seem to cover many cases, and pass without need for changes.

Links

PR #12881
Port assignment issue
Follow-on PR that will need this

PR Checklist

• updated test coverage
• [N/A] external facing docs updated
• [N/A] not a security concern