Expose feature flag to enable FIPS compliant build of AWS-LC.

[tobz]

It looks like the 0.27.0 release pulled in the necessary upstream crate bumps so that AWS-LC can be used as the rustls backend, and with a high enough version to also use the FIPS-compliant build... 🎉 . However, users still need to do the add-your-own-dependency-to-set-the-feature-flag-you-want hack if they're using hyper-rustls and want to use that FIPS-compliant mode.

I plan to whip up a quick PR to expose that, but wanted to file the issue so I don't forget. 😂

[djc]

Thanks for reporting -- happy to review a PR for this!