support native-tls driver

[nicholastmosher]

Here's what I've found after some research on this:

• First I set out to see where we have rustls as a dependency in all of our crates. I found that k8-client was a big offender (being linked to by many of our other crates), and that fluvio-future was another.
• On closer inspection, I found that k8-client was not actually using rustls at all, it can be removed without breaking any code.
  • One potential concern: k8-client has a hyper module and a native module to provide http clients. Currently, the hyper module is commented-out in lib.rs, meaning that it is completely unused. It turns out that rustls is a dependency of this hyper client, so if we ever plan on re-activating that module, this is something we will have to take care of.
• If removing rustls from k8-client is not a problem, then our only dependency on rustls and webpki are within the fluvio-future crate when the tls feature is activated. This will be my next point of research to see if we can use alternate dependencies to do whatever tls needs to do.

[sehz]

It is using rustls . However, we do want to preserve that capability. In order to do so we can put that under feature gate.

[sehz]

reason isahc was used because it had good integration with rustls. For native-tls, we could consider switch to hyper has good support

[nicholastmosher]

Right now I've been able to remove curl, openssl-sys, webpki, rustls, and fluvio-future from the dependencies of k8-client and continue building and testing successfully, even with --all-features and --all-targets. Right now the hyper module is broken (i.e. re-enabling it immediately causes a build break) so it's hard to determine which dependencies would need to stick around and how to put them into feature flags. I think we should just remove the unused dependencies for now and add them back as needed in the future if and when we want hyper support.

[sehz]

put hyper in the separate feature flag since it wasn't working previously

[sehz]

Done. Added feature flag for both rustls and native_tls. Use Hyper for Http Client