Meta file to watch for scenario changes

[Gamenot]

Is your feature request related to a problem? Please describe.
The base issue here is that we currently require scl scenario --clean in most cases to rebuild scenarios. This could be greatly sped up by skipping cases where things do not need to be rebuilt.

Describe the solution you'd like
I suggest a meta file that would maintain a hash of base scenario resource files:

• Map (e.g. map.xml)
• Scenario (e.g. scenario.py)
• requirements (e.g. requirements.txt)

When such files are noted to have changed it would trigger a rebuild of dependent scenario resources. This would be useful especially for very large maps and complex scenarios that take a long time to build.

[Adaickalavan]

Closed by #1764