Allow running the vault agent as a native sidecar

[domolitom]

Is your feature request related to a problem? Please describe.
It’s common for an application pod to start before the Vault Agent has finished mounting secrets, causing the app to restart a few times. Another issue that native sidecars could help resolve is discussed in this GitHub issue: #7112

Describe the solution you'd like
I would like to be able to inject the vault agent as a native sidecar which means it should run as an initContainer with restartPolicy: Always