deps: remove hyper-rustls/ring feature

[eliad-wiz]

Motivation

no reason to include the "ring" crate if aws-lc-rs is being used.

Solution

features are only additive, so they can't be removed once it's added (by any sub-crate).
avoid adding extra features that might not be used (e.g. in case of aws-lc-rs).

in order to make it optional we can add a new "ring" feature to the default features, so it can be avoided with default-features = false. however, i think letting the configure it as needed is a better approach.

please update if you do prefer to add a new default feature-flag (or some other approach) and i'll adjust the patch.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.

Project coverage is 76.1%. Comparing base (b21a4e5) to head (375899d).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
kube-client/src/client/auth/oauth.rs	0.0%	5 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1717     +/-   ##
=======================================
- Coverage   76.1%   76.1%   -0.0%     
=======================================
  Files         84      84             
  Lines       7860    7862      +2     
=======================================
  Hits        5977    5977             
- Misses      1883    1885      +2     

Files with missing lines	Coverage Δ
kube-client/src/client/auth/oauth.rs	0.0% <0.0%> (ø)

... and 2 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[clux]

i think we need (when using rustls);

• one of aws-lc-rs or ring
• webpki-roots optional, but orthogonal to this choice (so probably does not need to be checked here)

[eliad-wiz]

see my previous comment.
let's try adding cfg-if to make it a bit clearer

[clux]

i think we can avoid this extra change and dependency, and keep all logic as we had it before by introducing the new compile error up to top level (257 in oidc.rs).

#[cfg(all(feature = "rustls-tls", not(any(feature = "ring", feature = "aws-lc-rs"))))]
compile_error!("At least one of ring or aws-lc-rs feature must be enabled to use rustls-tls feature");

[clux]

mostly because the way it's indented now is also quite big and hard to extend, and we want to just bail out as soon as possible anyway.

besides, oidc.rs isn't even the client that is used for most things (that one comes from config_ext.rs + builder.rs and does the selection in tls.rs (which does not do this same if-else on providers).