Merge branch 'staging/metasploit-concern' into feature/extraction

MSP-9652
Extract Metasploit::Pro::Loading and initializer to Metasploit::Concern::Loader

MSP-9652

Metasploit::Concern::Loader is more generic as it will scan for concerns
under any root pathname and not just for mdm concerns.
Concern loading initializer

MSP-9652

Add config/initializer/load_concerns.rb, which will scan the
application and all engines for app/concerns and load those concerns
with Metasploit::Concern::Loader.
Ignore built gems

MSP-9652
Bump version

MSP-9652
Add usage docs

MSP-9652
Ignore .ruby-* files

MSP-9652
Work-around bug in shoulda-matchers 2.6.0

MSP-9652
Land #1

Merge branch 'feature/extraction' into staging/metasploit-concern
post merge step. updating prerelease