s/a/notify: add proper version handling to the notification protocol

[olivercalder]

Add versioning to the AppArmor notification protocol, do compatibility checks when registering a listener on the notify socket, and correctly validate incoming message versions against the listener version and set outgoing message versions correctly.

This work is tracked internally by https://warthogs.atlassian.net/browse/SNAPDENG-34337

[codecov]

Codecov Report

Attention: Patch coverage is 28.57143% with 55 lines in your changes missing coverage. Please review.

Project coverage is 78.23%. Comparing base (24a0034) to head (734c8a1).
Report is 95 commits behind head on master.

Files with missing lines	Patch %	Lines
sandbox/apparmor/notify/notify.go	0.00%	28 Missing ⚠️
sandbox/apparmor/notify/version.go	18.18%	18 Missing ⚠️
sandbox/apparmor/notify/message.go	47.05%	6 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #14914      +/-   ##
==========================================
+ Coverage   78.20%   78.23%   +0.02%     
==========================================
  Files        1151     1151              
  Lines      151396   152942    +1546     
==========================================
+ Hits       118402   119649    +1247     
- Misses      25662    25909     +247     
- Partials     7332     7384      +52     

Flag	Coverage Δ
unittests	78.23% <28.57%> (+0.02%)	⬆️

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