Replace BreadcrumbLevel and BreadcrumbType enums with String to accept arbitrary SDK values

[Dobrunia]

Breadcrumb type and level fields were defined as GraphQL enums with a fixed set of values. SDK users can send arbitrary strings (e.g. "debug" as a type), which causes GraphQL validation errors like Enum "BreadcrumbType" cannot represent value: "debug".

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 41.14%. Comparing base (0f8dad9) to head (c56ad1b).
⚠️ Report is 19 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #622       +/-   ##
===========================================
- Coverage   58.30%   41.14%   -17.16%     
===========================================
  Files          19       45       +26     
  Lines         518     2151     +1633     
  Branches       95      456      +361     
===========================================
+ Hits          302      885      +583     
- Misses        216     1199      +983     
- Partials        0       67       +67     

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