feat(operator): persist CA certificate and key in secrets and reuse o…

[Rucha0901]

Purpose of PR?:

Fixes #2755

Does this PR introduce a breaking change?
No

If the changes in this PR are manually verified, list down the scenarios covered::

• Verified that pkg/KubeArmorOperator cross-compiles cleanly with GOOS=linux go build ./....
• Implemented and verified the logic to extract existing CA certificate and CA private key from the kubearmor-controller-webhook-server-cert secret.

Additional information for reviewer? :
N/A

Checklist:

• Bug fix. Fixes feat(operator): persist CA certificate/key in secrets and reuse on rotation #2755
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• PR Title follows the convention of <type>(<scope>): <subject>
• Commit has unit tests (DCO signed off commit)
• Commit has integration tests

[vee1e]

@Rucha0901 a few things here

• please remove the unpinned image digests in favour of the pinned ones. this reduces the security of the dockerfile and is unrelated to the linked issue.
• you say the commit has unit tests but there aren't any _test.go files. add them, plesae don't put incorrect information in the PR description
• there's a stale TODO comment, Keep CA certificate in k8s secret which is the purpose of this entire PR. the comment should be removed, otherwise it reads as unfinished work.
• The 5-return-value pattern in GeneratePki (repeating four empty bytes.NewBuffer([]byte{}) per error branch) was already awkward before this PR and gets worse with a 5th value. This isn't a blocker, but a small helper (e.g. a zero-value struct or named error return) would clean it up if touched again.
• the Secrets().Get error handling doesn't distinguish "not found" from transient errors. Every other Get in this file uses IsNotfound(err) to tell "secret doesn't exist yet" apart from "API server hiccuped". This could result in new CA's being minted when not necessary (e.g during transient errors).

others can feel free to chime in, just giving my thoughts here.

[Rucha0901]

Hello @vee1e ,I am so sorry for this inconvenience. Give me some time I will fix all things.
Thank you!!

[Rucha0901]

@vee1e , As you asked I did the changes.
thank you!!