Consolidate EPP and sidecar TLS flag parsing

[andresllh]

What would you like to be added:

Consolidate TLS version and cipher suite parsing for the EPP server and pd-sidecar onto the existing helpers in k8s.io/component-base/cli/flag:

• flag.TLSVersion()
• flag.TLSCipherSuites()

Remove the duplicated tlsVersions, parseTLSVersion, and parseCipherSuites implementations from pkg/epp/server/options.go and pkg/sidecar/proxy/options.go, while retaining coverage for valid and invalid CLI values in both components.

Confirm whether the Kubernetes helpers' stricter handling of whitespace and empty cipher names is acceptable for sidecar YAML configuration, and document or test that behavior as appropriate.

Why is this needed:

PR #2676 adds TLS security profile flags to the pd-sidecar by following the existing EPP implementation. Both components would otherwise maintain equivalent TLS name-to-ID parsing even though k8s.io/component-base is already a direct dependency and provides these helpers.

[cyclinder]

I'd like to work on this, once #2676 lands — the sidecar half of the duplication only exists on that branch, so doing it now would just create another conflict.

Rough plan: switch both  Complete()  paths to  flag.TLSVersion()  /  flag.TLSCipherSuites()  and delete the local  tlsVersions  /  parseTLSVersion  /  parseCipherSuites . I'd keep the existing empty-value guards at the call sites so  ""  still means "not set" rather than picking up component-base's TLS 1.2 default.

On the stricter parsing: I'd take the Kubernetes behavior as-is — no trimming, empty names rejected — and add tests documenting it, plus the two legacy CHACHA20 aliases it accepts. Trimming YAML values before the call is easy to add if you'd rather keep the current tolerance; let me know which way you prefer.

/assign