feat(tracing): send both breadcrumbs and logs by default

[lcian]

Introduces a new function default_event_filter_with_logs which is the same as the default one but also sends logs for anything above INFO.
If the sentry crate is used with the logs feature and there's already a Hub active, grab enable_logs from the associated client and use the new default filter with logs if possible.
Users still need to opt into sending logs by enabling the feature flag and setting enable_logs: true, but this makes it easier if you don't want to set up a custom event filter, and it also makes the onboarding docs simpler.

An alternative to implement this would be to map tracing events to logs just by looking at the logs feature flag being enabled, but that way the user would still incur a performance penalty in the case they have enable_logs: false in their options, as we would anyways convert each tracing event to a Sentry log unnecessarily.

Close #871

[github-actions]

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📖	Do not forget to update Sentry-docs with your feature once the pull request gets approved.

Generated by 🚫 dangerJS against 480a59c

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.13%. Comparing base (4c4fc9d) to head (480a59c).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #878      +/-   ##
==========================================
- Coverage   73.14%   73.13%   -0.01%     
==========================================
  Files          64       64              
  Lines        7365     7375      +10     
==========================================
+ Hits         5387     5394       +7     
- Misses       1978     1981       +3     

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