Add support for keystores in VaultPKISecret

Hello,

Some apps need certificate stored in password protected PKCS12 keystore.

I currently use cert-manager Certificate with this config for creating password protected keystore.

~~~
---
apiVersion: cert-manager.io/v1
kind: Certificate
metadata:
name: certificate-example
spec:
commonName: example
issuerRef:
group: cert-manager.io
kind: ClusterIssuer
name: issuer
keystores:
pkcs12:
create: true
passwordSecretRef:
key: password
name: keycloak-pkcs12
secretName: certificate-secret
~~~

That add a **keystore.p12** and a **truststore.p12** keys to the created Kubernetes secret which can be mount as Kubernetes volume.

Can you add PKCS12 keystores support to VaultPKISecret ?

Thank's.

Start by locating the VaultPKISecret implementation and its Kubernetes Secret output handling. Compare the requested cert-manager keystores.pkcs12 configuration, including passwordSecretRef, with the existing resource behavior. Done means VaultPKISecret can produce password-protected keystore.p12 and truststore.p12 entries in a mounted Kubernetes Secret.

Written by the indexing model from the issue text.