chore: alembic script to create notifications and recipients tables

[blenzi]

This PR adds an alembic script to create notifications and recipients tables. The db in dev already contains those, while in prod it is not the case. So the migration is supposed not to overwrite the existing tables.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 94.95%. Comparing base (0ffbf38) to head (8a955c0). Report is 42 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #309   +/-   ##
=======================================
  Coverage   94.95%   94.95%           
=======================================
  Files          63       63           
  Lines        1505     1505           
=======================================
  Hits         1429     1429           
  Misses         76       76           

Flag	Coverage Δ
unittests	94.95% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[frgfm]

Closing as this was for the legacy data model, feel free to reopen if I missed something!