feat(seer onboarding): add Seer onboarding endpoint

[srest2021]

fixes CW-48

Add an endpoint OrganizationSeerOnboardingEndpoint to handle Seer onboarding settings (to be used in the wizard). This endpoint calls the onboarding_seer_settings_update function.

Currently only supports RCA settings and project repo mappings. But per the ticket we could always add code review settings and the endpoint is named/designed generally.

[linear]

CW-48 Add backend API to save RCA onboarding values

[github-actions]

🚨 Warning: This pull request contains Frontend and Backend changes!

It's discouraged to make changes to Sentry's Frontend and Backend in a single pull request. The Frontend and Backend are not atomically deployed. If the changes are interdependent of each other, they must be separated into two pull requests and be made forward or backwards compatible, such that the Backend or Frontend can be safely deployed independently.

Have questions? Please ask in the #discuss-dev-infra channel.

[Mihir-Mavalankar]

Function call and input formats look good.

[JoshFerge]

API changes look good! will let others review + approve on the business logic! thank you!

[billyvg]

LGTM

[codecov]

Codecov Report

❌ Patch coverage is 97.50000% with 2 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...try/seer/endpoints/organization_seer_onboarding.py	97.46%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #104818      +/-   ##
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+ Coverage   80.41%    80.42%   +0.01%     
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  Files        9386      9386              
  Lines      403019    403002      -17     
  Branches    25929     25908      -21     
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+ Hits       324075    324134      +59     
+ Misses      78496     78420      -76     
  Partials      448       448