WIP Msg filter

[JakeHartnell]

Was feeling inspired on the plane, this is very much WIP and should be considered a strawman. Want to make sure we get the API and filtering right before we actually hook it up to a proposal module.

Feedback needed, hopefully the new cw-msg-filter README provides a good overview of current usage and API.

Hopefully Closes #694

Close this PR if someone makes a better version.

[codecov]

Codecov Report

Attention: Patch coverage is 92.23986% with 44 lines in your changes missing coverage. Please review.

Project coverage is 96.61%. Comparing base (75272b9) to head (83818f5).

Files	Patch %	Lines
packages/cw-msg-filter/src/lib.rs	92.23%	44 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##           development     #872      +/-   ##
===============================================
- Coverage        96.64%   96.61%   -0.04%     
===============================================
  Files              240      241       +1     
  Lines            65294    65862     +568     
===============================================
+ Hits             63106    63631     +525     
- Misses            2188     2231      +43     

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