an API/function/spec that will let us execute `kubectl debug` ephemeral pods

[adamancini]

Describe the rationale for the suggested feature.

to build on the exec collector, perhaps, we should start to support ephemeral containers executed by kubectl debug

ephemeral containers can attach to existing pods, with an image of choice, to run commands and extract data, and can also be executed at the Node scope for the same

Describe the feature

existing spec

- exec:
        name: mysql-version
        selector:
          - app=mysql
        namespace: default
        command: ["mysql"]
        args: ["-V"]
        timeout: 5s

maybe we could support something like

- exec:
        name: mysql-version
        ephemeralPod:
            image: nicolaka/netshoot
            target: mysql
            attach: false
        selector:
          - app=mysql
        namespace: default
        command: ["mysql"]
        args: ["-V"]
        timeout: 5s
- exec:
        name: htop
        ephemeralPod:
            image: nicolaka/netshoot
            target: node/hostname
            attach: false
        command: ["htop"]
        timeout: 5s