Add custom breadcrumb data source

[fractalwrench]

Goal

Implements the capture of custom breadcrumbs via the DataSource interface which allows them to be sent as OTel data types in the session payload. It's important to note this does not alter the session payload yet. The LegacyCustomBreadcrumbDataSource will continue to add directly to the payload.

#488 contains the changeset for enabling the new data capture mechanism. This uncouples work & allows us to merge more without blocking changes.

Testing

Added a unit test.

[codecov]

Codecov Report

Attention: Patch coverage is 76.92308% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 79.34%. Comparing base (026492f) to head (4ff32a8).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #487      +/-   ##
==========================================
+ Coverage   79.31%   79.34%   +0.03%     
==========================================
  Files         387      388       +1     
  Lines       10561    10577      +16     
  Branches     1571     1573       +2     
==========================================
+ Hits         8376     8392      +16     
  Misses       1551     1551              
  Partials      634      634              

Files	Coverage Δ
...racesdk/capture/crumbs/EmbraceBreadcrumbService.kt	96.55% <100.00%> (ø)
...cesdk/capture/crumbs/CustomBreadcrumbDataSource.kt	93.75% <93.33%> (+43.75%)	⬆️
...capture/crumbs/LegacyCustomBreadcrumbDataSource.kt	50.00% <50.00%> (ø)

... and 2 files with indirect coverage changes

[lucaslabari]

LGTM

[bidetofevil]

LGTM