Mutating admission webhook and CRD

[worldtiki]

Describe the feature

Looking at the example in the documentation, most of the configs are just boilerplate to run Mittens than actual configs related to the warmup process.

This is actually worse if we add things like image pull secrets, resources, etc.

My proposal is to create a mutating admission webhook for Kubernetes that would react to a label (xyz-mittens-injection: true) and inject a Mittens sidecar when a new pod with this label is created.
The webhook would search for either a custom resource or a config map for that deployment where users would provide the flags required to run mittens (http requests, duration of the warmup, etc.) and use that information to inject the Mittens sidecar.

Rational

Reduce friction to adopt Mittens.