Remove OpenSSL dependency; use rustls-tls exclusively

[Krechals]

What did you change, and why?

Remove default-tls and native-tls from reqwest features and set default-features = false, keeping only rustls-tls.

This removes the openssl, openssl-sys, and native-tls transitive dependencies. The binary now only links against libc, libm, and libgcc_s, which are present on all Linux distributions. Previously the binary required libssl.so.1.1, which does not exist on Ubuntu 24.04 (OpenSSL 3 only), causing a startup failure:

click: error while loading shared libraries: libssl.so.1.1: cannot open shared object file: No such file or directory

The source code already calls .use_rustls_tls() explicitly on every reqwest client (k8s.rs), so native-tls was never used at runtime. Cargo.lock confirms no transitive dependency pulls in openssl, openssl-sys, or native-tls either.

How do you know it works?

Built locally on Ubuntu 24.04. ldd output before and after:

Before: libssl.so.1.1 => not found

After:

linux-vdso.so.1
libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1
libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6

Binary smoke-tested: click --help works correctly.