feat: add feature flag to support rustls-tls

[ameijboom]

Due to the dependency on reqwest with it's default options, we have no way to replace openssl with rustls, which is an issue for our projects.

With this PR, I've added a feature flag that replaces openssl with rustls, while leaving the default on openssl. This ensures no breaking changes with previous versions and allows anyone to choose between their preferred TLS library.

Checklist

• I have read the contributing guidelines and signed the CLA.
• I have referenced an issue containing the design document if my change introduces a new feature.
• I have read the security policy.
• I confirm that this pull request does not address a security vulnerability.
  If this pull request addresses a security vulnerability,
  I confirm that I got approval (please contact [email protected]) from the maintainers to push the changes.
• I have added tests that prove my fix is effective or that my feature works.
• I have added the necessary documentation within the code base (if appropriate).

[aeneasr]

Please see https://github.com/ory/client-rust?tab=readme-ov-file#generation

[ameijboom]

Ah I see. Will immediately check.