feat(anomaly detection):preview chart proxy api endpoint

[mifu67]

Build out the preview chart proxy endpoint. Calls a placeholder function.

[codecov]

Codecov Report

Attention: Patch coverage is 57.44681% with 20 lines in your changes missing coverage. Please review.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...try/api/endpoints/organization_events_anomalies.py	55.81%	19 Missing ⚠️
...seer/anomaly_detection/get_historical_anomalies.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #77813       +/-   ##
===========================================
+ Coverage   61.67%   78.09%   +16.42%     
===========================================
  Files        6970     6982       +12     
  Lines      309249   309727      +478     
  Branches    50629    50680       +51     
===========================================
+ Hits       190730   241891    +51161     
+ Misses     112656    61401    -51255     
- Partials     5863     6435      +572