fix: flatten searchable os distribution fields

[JoshuaMoelans]

update to #69865
To search the distribution fields, we cannot have them in a hierarchy os.distribution.name, we instead need them flattened to os.distribution_name

This is part of reworking the following native-SDK PR: getsentry/sentry-native#963

The update is also tracked on the docs side: getsentry/sentry-docs#11936
And on Relay: getsentry/relay#4292

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/sentry/rules/conditions/event_attribute.py	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #81297      +/-   ##
==========================================
+ Coverage   80.35%   80.36%   +0.01%     
==========================================
  Files        7221     7220       -1     
  Lines      319593   319764     +171     
  Branches    20783    20783              
==========================================
+ Hits       256800   256988     +188     
+ Misses      62398    62381      -17     
  Partials      395      395              

[kahest]

@narsaynorath added you as reviewer since you're familiar with #69865 but pls add other folks as needed 🙏

[narsaynorath]

Looks good to me. iirc when we last made this change it was because nested contexts weren't assigned a key properly in clickhouse, so since we're reducing the level of nesting, this should match up properly