Fix regions and add clarity in Lambda Layer release workflow

[jj22ee]

Issue #, if available:

• Original issue in Python Lambda release Fix regions and add clarity in Lambda Layer release workflow aws-otel-python-instrumentation#458
  • The new regions should be added to the default list, not the commercial region env variable

Description of changes:

• Cherry-pick Fix regions and add clarity in Lambda Layer release workflow #1185 from main

    Remove new regions from COMMERCIAL_REGIONS
    Rename COMMERCIAL_REGIONS to LEGACY_COMMERCIAL_REGIONS
    Add comments for clarity

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.