Configurable failurePolicy for the MutatingWebhook of the vault agent injector

[orirawlings]

Is your feature request related to a problem? Please describe.
We observe some occasional race conditions between recreation of the vault agent injector pod (for ex. due to node disruption) and the creation of other pods that expect a vault agent to be injected. Currently, the MutatingWebhook is configured with the default failurePolicy (i.e. Ignore) so when these pods are created while the injector is unavailable, they proceed through creation without the mutation. These pods often run applications that CrashLoopBackoff indefinitely because necessary access to secrets is never established.

Describe the solution you'd like
We'd like to be able to temporarily block pod creation when vault agent injector is unavailable, and as such, we'd like to expose the configuration of the MutatingWebhook's failurePolicy in the chart values.

Describe alternatives you've considered
None

Additional context
None