fix: Add alerts_count, affected_services and sources fields to the Incident

[VladimirFilonov]

Add alerts_count, affected_services and sources fields to the Incident and pre-population logic for them on adding alerts to the incident

Closes #1472

📑 Description

The incidents list page performed poorly when there were a large number of alerts in the incidents. That happened because alerts count, affected services and sources were calculated in runtime.

This PR changes this behavior to pre-calculated data for incidents

✅ Checks

• My pull request adheres to the code style of this project
• My code requires changes to the documentation
• I have updated the documentation as required
• All the tests have passed

ℹ Additional Information

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
keep	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Aug 8, 2024 8:24am

[talboren]

I have a few comments, mostly around dialect specific SQL functions that could be problematic in the future (or even now).
Maybe the ideal case here is to have some worker doing those calcs in the background? just thinking out loud, idk.

[codecov]

Codecov Report

Attention: Patch coverage is 21.21212% with 52 lines in your changes missing coverage. Please review.

Project coverage is 37.36%. Comparing base (c0be6a5) to head (b8e5f12).
Report is 6 commits behind head on main.

Files	Patch %	Lines
keep/api/core/db.py	10.81%	33 Missing ⚠️
tests/conftest.py	17.64%	14 Missing ⚠️
keep/api/core/db_utils.py	28.57%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1473       +/-   ##
===========================================
- Coverage   68.38%   37.36%   -31.03%     
===========================================
  Files         112       28       -84     
  Lines        9288     2671     -6617     
===========================================
- Hits         6352      998     -5354     
+ Misses       2936     1673     -1263     

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[talboren]

LGTM!