Support ECDSA P-256 certificates

[ron1]

Describe the problem/challenge you have

I need to bootstrap Linkerd with an ECDSA P-256 certificate.

Describe the solution you'd like

I would like to use the secretgen controller to create a ECDSA P-256 certificate for use by graduated CNCF project Linkerd. Linkerd does not support the RSA certs created by the secretgen controller.

Anything else you would like to add:

[cppforlife]

@ron1 that would be good. do you happen to know some recommended ways to generate that type of certificate in go?

[cppforlife]

ah i see some prior art in here: https://go.dev/src/crypto/tls/generate_cert.go

[ron1]

You can also take a look at this linkerd-cli function that generates a ecdsa key: https://github.com/linkerd/linkerd2/blob/b9aa32f9b20057c7166347825428e53525962b9c/pkg/tls/ca.go#L145