Add support for EC private keys

[farcaller]

Motivation

Allows to use kube-rs with e.g. k3s and k3d default installs that use the Sec1 private keys.

Solution

This depends on

• Add support for EC private keys rustls/pemfile#5
• Support SEC1-format EC keys via PKCS8 conversion rustls/rustls#998
• waiting for the rustls release to catch up

[farcaller]

Note that this PR alone won't be enough to make k3s work as the default kubeconfig uses IP addresses. The relevant feature request is here: briansmith/webpki#54.

[clux]

Realised that the jobs here never ran, hence the sudden activity. The red deny ❌ looks like what was fixed in master.

[farcaller]

The deps caught up, this is now ready for review.

[clux]

CI test failure remaining on cargo-deny: hyper-rustls brings in an older version of rustls-pemfile.
Looks like this will be resolved by rustls/hyper-rustls#165

[clux]

Can confirm that this works on k3d (with the old dns bypass) 🎉

Earlier error:

• Error: rustls tls error: identity PEM is missing a private key: the key must be PKCS8 or RSA/PKCS1

New bypassable error:

• Error: failed to perform initial object list: HyperError: error trying to connect: invalid dnsname

Bypass: #153 (add localhost entry to /etc/hosts and change the kube/config cluster.server url to use localhost)

@farcaller : it nothing major, all the real tests pass, and the pr works perfectly 👍 . the failing check is cargo-deny which you can run locally with make deny - it's just trying to limit multiple versions of dependencies in the dependency tree. It's possible we can put a bypass for it (this is an important fix after all), but it would be nicer if hypertls-rustls made a release with the updated pemfile dep.

[clux]

We will add an override file for this after making a 0.69 release (today/tomorrow), and merge this right after. then hopefully the ecosystem acquires internal consistency in the mean time (or else 0.70 release will be released with the override).

in either case don't want to delay this too much, but want to try to keep the set of dependencies consistent

[clux]

Override added so all checks passing now. Merging.

Thanks again!