[FIX] prioritize cli options over yaml

[maryamhonari]

Proposed change(s)

steps to reproduce the bug:

1. run exp1 for 1M steps
2. initialize exp2 from last one with yaml["checkpoint_settings"]["initialize_from"] and continue running for eg. 200k
3. resume exp2  from cmd and the step count continues from 1M instead of 200k

solution: checkpointSetting class now prioritize the command line arguments (resume or initialize_from for now) over conflicting yaml options. yaml option is nuke with a warning

Useful links (Github issues, JIRA tickets, ML-Agents forum threads etc.)

Types of change(s)

• Bug fix
• New feature
• Code refactor
• Breaking change
• Documentation update
• Other (please describe)

Checklist

• Added tests that prove my fix is effective or that my feature works
• Updated the changelog (if applicable)
• Updated the documentation (if applicable)
• Updated the migration guide (if applicable)

Other comments

[ervteng]

Do we need a test to check if they were both set in the YAML but not the CLI? I think we can do this in the test_settings.py.

[ervteng]

Forgot in my last approval - add this bug fix to the CHANGELOG.md file and reference the PR before merging.