Disallow deleting or moving the last server in a Cache Group used by a topology

[zrhoffman]

What does this PR (Pull Request) do?

• This PR fixes Traffic Ops should prohibit deleting the last Server in a Cache Group that is assigned to a Topology #5154
• Keeps you from deleting a Server from a CacheGroup used by a Topology or moving a Server from a CacheGroup used by a Topology if it means that Cache Group would no longer have any servers in it
• Adds the cachegroupName query parameter to GET /api/3.0/servers

Which Traffic Control components are affected by this PR?

• Documentation
• Traffic Control Client
• Traffic Ops

What is the best way to verify this PR?

1. Run the API tests

2. Test manually:
   For DELETE /api/3.0/servers/{{id}}:

   1. Make a Cache Group
   2. Add only 1 Server to the Cache Group
   3. Make a Topology with that Cache Group
   4. Delete the Server (should fail)

   For PUT /api/3.0/servers/{{id}}:

   1. Make a Cache Group
   2. Add only 1 Server to the Cache Group
   3. Make a Topology with that Cache Group
   4. Move the Server to a different Cache Group (should fail)

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)

Additional Information

[mitchell852]

performed manual tests via TP via the API. worked great. didn't look at code however.