fix(sdk): Loosen reqwest feature flags to avoid pulling aws-lc-sys

[procr1337]

Previously, matrix-sdk would pull aws-lc-sys as a transitive dependency via reqwest's rustls feature, even if downstream users otherwise rely on ring. rustls-no-provider is the provider-agnostic alternative, which is now used instead.

This is a breaking change because downstream users now have to pick a provider explicitly, via a reqwest feature flag or by manually registering a rustls provider.

If preferred, we can introduce a new feature flag for the previous behavior, and make it a default. That way it can be deselected manually.

• I've documented the public API changes in the appropriate changelog files
• This PR was made with the help of AI.

[codspeed-hq]

Merging this PR will not alter performance

✅ 27 untouched benchmarks
⏩ 23 skipped benchmarks¹

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_{Comparing procr1337:remove-reqwest-feature-flag (59a9e28) with main (023f5bd)}

Footnotes

1. 23 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (main@023f5bd). Learn more about missing BASE report.
✅ All tests successful. No failed tests found.

Additional details and impacted files

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  Hits            ?    99530           
  Misses          ?     7354           
  Partials        ?     3772           

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