Backport of api: remove mapstructure tags fromPort struct into release/1.3.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #12916 to be assessed for backporting due to the inclusion of the label backport/1.3.x.

WARNING automatic cherry-pick of commits failed. Commits will require human attention.

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

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This PR solves a defect in the deserialization of api.Port structs when returning structs from theEventStream.

Previously, the api.Port struct's fields were decorated with both mapstructure and hcl tags to support the network.port stanza's use of the keyword static when posting a static port value. This works fine when posting a job and when retrieving any struct that has an embedded api.Port instance as long as the value is deserialized using JSON decoding. The EventStream, however, uses mapstructure to decode event payloads in the api package. mapstructure expects an underlying field named static which does not exist. The result was that the Port.Value field would always be set to 0.

Upon further inspection, a few things became apparent.

• The struct already has hcl tags that support the indirection during job submission.
• Serialization/deserialization with both the json and hcl packages produce the desired result.
• The use of of the mapstructure tags provided no value as the Port struct contains only fields with primitive types.

This PR:

• Removes the mapstructure tags from the api.Port structs
• Updates the job parsing logic to use hcl instead of mapstructure when decoding Port instances.

Closes #11044

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