Switch to rustls in generated CLI

[wafflespeanut]

Right now, we're using OpenSSL for custom TLS configuration. But, we can also do that in rustls and reqwest does support that backend, which is what we should switch to for the CLI to be platform-agnostic.

[somehowchris]

Has there been some progress outside this issue? Would love to contribute

I'm looking into doh & rustls. Is it possible to provide a custom client? not only for the cli but for anything else