Allow extensions to hook into container creation

[cedricziel]

Describe the solution you'd like A docker extension should be able to hook into the creation of objects in the engine.

An extension could thus apply mutations or reject a specific configuration. This could be useful to inject environment variables, enforce compliance regulations or plain reject certain configurations.

Describe alternatives you've considered

Kubernetes knows about the concept of Mutating Webhooks to allow similar behavior.

Additional context It would be nice if an extension containing an o11y agent could automatically configure workloads based on their definition.