Add support for MustObeyClient Module API

[KarthikSubbarao]

This PR adds support for MustObeyClient Module API.

The purpose of this API is for Modules to handle commands / callbacks knowing whether commands are arriving from the primary client or AOF client and should never be rejected.

A use case is that Modules can have validation logic in command handlers which only should be executed on primary nodes. Replica nodes must obey commands replicated.

Will add tests once/if we agree on the use case and syntax of the Module API

[codecov]

Codecov Report

Attention: Patch coverage is 25.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 70.95%. Comparing base (2d0b8e3) to head (c53e3ac).

Files with missing lines	Patch %	Lines
src/module.c	25.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #1582      +/-   ##
============================================
+ Coverage     70.94%   70.95%   +0.01%     
============================================
  Files           121      121              
  Lines         65132    65136       +4     
============================================
+ Hits          46207    46218      +11     
+ Misses        18925    18918       -7     

Files with missing lines	Coverage Δ
src/module.c	9.61% <25.00%> (+0.01%)	⬆️

... and 11 files with indirect coverage changes