feat(cli): cli as k8s deployment for debugging

[sakoush]

What this PR does / why we need it:

This PR creates a docker image seldonio/seldon-cli with Seldon CLI prepackaged in it. Users can then deploy this image in Kubernetes alongside Core 2 installation in the same namespace.

This PR also factors out kafka config code into a top level component so that it can be used by the cli and especially in a Kubernetes deployment where it can have access to seldon-kafka ConfigMap for consumer config.

We have disabled also Seldon CLI control plane operations (e.g. load and unload) by default as they can cause inconsistencies in Kubernetes installation. They can be re-enabled with the flag --force.

Docs have been also adjust and perhaps it would be a good entrypoint to review the changes of this PR. Link to rendered docs here.

Which issue(s) this PR fixes:

Fixes Infra-1269 (internal)

Special notes for your reviewer:

• Unit tests have been added for this change.
• CI changes added to include tests and builds of the new top level component.

[driev]

Looks good - left a few small comments.