feat(transport): add SENTRY_LINK_CURL option

[jpnurmi]

Add SENTRY_LINK_CURL CMake option (inspired by SENTRY_LINK_PTHREAD) to choose whether the curl transport links libcurl directly or resolves it at runtime with dlopen/dlsym. Keep direct linking enabled by default.

The linked and runtime-loaded paths use the same curl call table, so the request logic remains shared.

If the runtime dependency is not satisfied:

[sentry] WARN failed to load libcurl.so.4: libcurl.so.4: cannot open shared object file: No such file or directory
[sentry] WARN failed to initialize transport
[sentry] WARN `sentry_init` failed

See:

• Native: optimize backend startup on Linux #1852

[github-actions]

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

Generated by 🚫 dangerJS against 2117505

[codecov]

Codecov Report

❌ Patch coverage is 79.76190% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.98%. Comparing base (f2f784c) to head (2117505).
⚠️ Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1954      +/-   ##
==========================================
+ Coverage   75.93%   75.98%   +0.04%     
==========================================
  Files          94       94              
  Lines       22161    22180      +19     
  Branches     3936     3937       +1     
==========================================
+ Hits        16829    16854      +25     
+ Misses       4445     4440       -5     
+ Partials      887      886       -1     

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[limbonaut]

Partially reviewed, I'll give it another look in a bit!

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[limbonaut]

Looks good!