chore(anomaly detection): add Seer delete call for if alert has associated incident

[mifu67]

Currently, these alerts are not deleted from the DB, so the post_delete() will not fire.

[codecov[bot]]

Codecov Report

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

:white_check_mark: All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #78564      +/-   ##
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+ Coverage   78.12%   78.13%   +0.01%     
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  Files        7089     7089              
  Lines      312555   312594      +39     
  Branches    51051    51059       +8     
==========================================
+ Hits       244181   244250      +69     
+ Misses      62007    61965      -42     
- Partials     6367     6379      +12