Deprecate traffic_monitor/stats

[mhoppa]

What does this PR (Pull Request) do?

• This PR fixes Rewrite /traffic_monitor/stats to Go #3846

Which Traffic Control components are affected by this PR?

• Documentation
• Traffic Ops

What is the best way to verify this PR?

Make request to route and make sure deprecation notice is returned and then build docs to ensure the deprecation message is correctly formatted.

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 OR I have explained why tests are unnecessary
• This PR includes documentation OR I have explained why documentation is unnecessary
• This PR includes an update to CHANGELOG.md OR such an update is not necessary
• This PR includes any and all required license headers
• This PR ensures that database migration sequence is correct OR 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

[ocket8888]

Manual requests show deprecation notices in API response payloads, docs are accurate and build without errors or warnings.

[ocket8888]

Need to fix conflicts before merge, though

[mhoppa]

Done