feat: Use feature flag to allow rustls-no-provider with reqwest

[SanchayanMaity]

This allows applications or other users of the crate to not bring aws-lc-rs as a dependency due to cargo feature unification and let a user of the crate install a crypto provider manually for use by reqwest.

See https://docs.rs/rustls/latest/rustls/#cryptography-providers for details.

When opting into reqwest/rustls-no-provider, application must install a crypto provider. For example, rustls::crypto::ring::default_provider().install_default().

Proposed changes

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update or tests (if none of the other choices apply)

Checklist

• I have read the CONTRIBUTING.md doc
• I have added tests and/or examples that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

[SanchayanMaity]

For some more context on this change,

We use the deepgram SDK in GStreamer for transcribing. We have avoided pulling in aws-lc-rs as a dependency for various reasons. Because of feature unification in cargo, a dependency enabling aws-lc-rs (reqwest feature flag rustls in this case here) results in it becoming part of the dependency chain.

reqwest already allows control over this and so do other crates like quinn. The current change should not affect any downstream users while allowing other users leeway in opting for a different crypto provider.