Enhancement: Use self-signed certs for webhook server

[senthilrch]

Kube-fledged installation currently relies on Kubernetes CertificateSigningRequest to generate the server certificate for the webhook server. This creates problems:-

• The stable v1 version of CertificateSigningRequest doesn't supports signer kubernetes/legacy-unknown
• The supported in-built signers are not usable to generate a server certificate. There's support only for client certificates
• On clusters that have only v1 enabled, it is impossible to generate server certificate.
• Bash script is used to generate certificate, so installing via GitOps (e.g. ArgoCD) is not fully supported.
• Ref issue Deployment using the Operator 0.8.0 #75 , issue Deployment via Helm chart fail #76

The solution is to generate self-signed certificate for the webhook server and add the CA bundle to the validatingwebhookconfiguration, using init container or as init method within the webhook server.