Enable usage of dynamic leaf certificates using a certificate resolver

[Techassi]

Currently to use TLS with webhooks, you have to manually mount a volume with the CA.

This PR: #736 adds a module to the framework that supports creating CAs and leaf certificates. Here we could just call the code to generate the certs and call the server, but then there is no way for them to be swapped out if they expire.

This ticket is about writing code to - instead of mounting a single cert - resolve a cert dynamically, allowing us to swap out expired certs while the Webhook server is running.

This resolver will be used by the stackable-webhook crate.

Follow up of #736.

Acceptance criteria

• This TODO is resolved, and the AutoGenerate feature on the CA for the webhook works