Combine CDN in a Box Dockerfiles using build stage targets where possible

[zrhoffman]

What does this PR (Pull Request) do?

Currently, if you try to build the trafficmonitor-debug, trafficops-debug, and trafficstats-debug images without the trafficmonitor, trafficops, and trafficstats existing,

docker-compose -f docker-compose.yml -f optional/docker-compose.debugging.yml build --parallel trafficops

it will fail to build with an error like

 ---> 82cad2818884
Step 5/6 : FROM trafficops
pull access denied for trafficops, repository does not exist or may require 'docker login': denied: requested access to the resource is denied
Service 'trafficops' failed to build

because you need to build those images first. You can get around that by simply attempting to build everything twice:

docker-compose -f docker-compose.yml -f optional/docker-compose.debugging.yml build --parallel
docker-compose -f docker-compose.yml -f optional/docker-compose.debugging.yml build --parallel

But updating RPMs in the debug images is still annoying because it requires building everything twice in this way. This PR fixes that behavior.

This PR

• Makes the Traffic Monitor, Traffic Ops, and Traffic Ops debug images build stage targets within the non-debug Dockerfiles

• Removes the trafficmonitor-nondebug, trafficops-nondebug, and trafficstats-nondebug services from the docker-compose.debugging.yml compose file

• Makes edge build the edge target of cache/Dockerfile and makes mid-01 and mid-02 build the mid target of cache/Dockerfile

• Adds the ability to debug the CDN in a Box enroller

• This PR is not related to any Issue

Which Traffic Control components are affected by this PR?

• CDN in a Box

What is the best way to verify this PR?

• Untag the trafficmonitor, trafficops, and trafficstats images and then verify that running

  docker-compose -f docker-compose.yml -f optional/docker-compose.debugging.yml build --parallel

  succeeds

• Following the debugging documentation, set a breakpoint in enroller.go and try to hit it

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

The following criteria are ALL met by this PR

• CiaB changed only, tests unnecessary
• This PR contains documentation
• An update to CHANGELOG.md is unnecessary
• This PR includes any and all required license headers
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)

[tcfdev]

Here's a few thoughts and notes based on reading the changes. I'm working on validating functionality separately.

[tcfdev]

Confirmed debugging possible in Goland and VSCode.

[tcfdev]

Code reviewed and functionality tested. LGTM!

Approved!