Rewrite /cachegroups/{id}/unassigned_parameters to golang

[mhoppa]

What does this PR (Pull Request) do?

This PR rewrites the /cachegroups/{id}/unassigned_parameters endpoint to Go

• This PR fixes Rewrite /cachegroups/{{id}}/unassigned_parameters to Go #3807

Which Traffic Control components are affected by this PR?

• Documentation
• Traffic Ops

What is the best way to verify this PR?

Bring up TO locally and hit the endpoint to ensure parity between perl implementation and newly written Golang implementation

The API tests and/or unit tests for TO can be run to verify the PR.

If this is a bug fix, what versions of Traffic Control are affected?

The following criteria are ALL met by this PR

• This PR includes tests
• This PR includes documentation
• This PR includes an update to CHANGELOG.md
• This PR includes any and all required license headers
• This PR does not include a database migration
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)

[asf-ci]

Refer to this link for build results (access rights to CI server needed):
https://builds.apache.org/job/trafficcontrol-PR/4206/
Test PASSed.

[ocket8888]

Builds and runs fine, manual testing confirms it works, automated unit and client tests make sense and pass