meta: add repro guide and needs-repro automation

[jamescrosswell]

Summary

Resolves #4105

• Add info on how to provide minimal repro #4105

Changes

• .github/repro.md – New guide explaining what a minimal reproduction is, why we ask for one, how to create it, and what to avoid. Adapted from the .NET MAUI repro guide but tailored for the Sentry .NET SDK.

• .github/ISSUE_TEMPLATE/bug_report.yml – Added a markdown block at the top of the bug report form linking to the new guide, and updated the "Steps to Reproduce" field description to reference the guide.

• .github/workflows/needs-repro.yml – New GitHub Actions workflow that automatically posts a comment with repro instructions and a link to the guide whenever the Needs Reproduction label is added to an issue.

#skip-changelog

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Semver Impact of This PR

⚪ None (no version bump detected)

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.95%. Comparing base (2079493) to head (6763ae0).
⚠️ Report is 47 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4975      +/-   ##
==========================================
+ Coverage   73.86%   73.95%   +0.08%     
==========================================
  Files         496      497       +1     
  Lines       17951    17966      +15     
  Branches     3516     3516              
==========================================
+ Hits        13259    13286      +27     
+ Misses       3833     3823      -10     
+ Partials      859      857       -2     

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[Flash0ver]

I believe feat is not quite the right commit label.

I think meta would fit better.
See also https://develop.sentry.dev/engineering-practices/commit-messages/

[jamescrosswell]

I think meta would fit better.

Done.

I also simplified the instructions. There was a lot of contnet in there anticipating problems / anger with us asking for a repro. They maybe get that at Microsoft but we've never really had a problem with this tbh, so I think we should leave it out initially. If we start to get push back when asking for minimal repros, we can add it back in later.

[Flash0ver]

I like the simplification.