fix: DIA-1061: Start Training should send START_TRAINING event as webhook instead of PROJECT_UPDATE

[makseq]

Change has impacts in these area(s)

(check all that apply)

• Product design
• Backend (Database)
• Backend (API)
• Frontend

Describe the reason for change

Start Training button on Model settings page sends PROJECT_UPDATE event and it's not possible to distinguish when Start Training really was called.

What does this fix?

ML backend model method fit(..., event, ...) will be able to distinguish the right training event.

What is the current behavior?

ML backend model method fit(..., event, ...) receives PROJECT_UPDATE as event and this can be triggered on any project change event.

[netlify]

✅ Deploy Preview for heartex-docs canceled.

Name	Link
🔨 Latest commit	e532c95
🔍 Latest deploy log	https://app.netlify.com/sites/heartex-docs/deploys/6629c3669fc1550008043dca

[netlify]

✅ Deploy Preview for label-studio-docs-new-theme canceled.

Name	Link
🔨 Latest commit	e532c95
🔍 Latest deploy log	https://app.netlify.com/sites/label-studio-docs-new-theme/deploys/6629c3667f92bb000828f369

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.92%. Comparing base (9f1cba7) to head (e532c95).
Report is 18 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #5761   +/-   ##
========================================
  Coverage    75.92%   75.92%           
========================================
  Files          158      158           
  Lines        13356    13356           
========================================
  Hits         10140    10140           
  Misses        3216     3216           

Flag	Coverage Δ
pytests	75.92% <ø> (ø)

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

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.