Add notifications module

[albireox]

Mostly copied from lvm-api but without database insertion. Added test.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.3%. Comparing base (9c7feb4) to head (75234ef).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main     #12     +/-   ##
=======================================
+ Coverage   90.3%   91.3%   +1.1%     
=======================================
  Files         12      13      +1     
  Lines        768     845     +77     
  Branches     105     114      +9     
=======================================
+ Hits         693     771     +78     
  Misses        33      33             
+ Partials      42      41      -1     

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