Add "Standalone Components" section to "Installing Kubeflow"

[thesuperzapper]

This PR is intended as an alternative to the proposal from @andreyvelich in #3724.

The goal of this PR is to reduce confusion, while still meeting the request of @andreyvelich to tell users that some components may be installed separately.

The main change is the addition of a "Standalone Components" section on the "Installing Kubeflow".

This "Standalone Components" section has a table which lists if each component of Kubeflow is able to be deployed "standalone", that is, without the rest of the platform.

/assign @kubeflow/wg-notebooks-leads @kubeflow/wg-pipeline-leads @kubeflow/wg-training-leads @kubeflow/wg-data-leads @kubeflow/release-team @kubeflow/kubeflow-steering-committee @kubeflow/wg-deployment-leads

Screenshot

Here is a screenshot of the updated "Installing Kubeflow" page:

[google-oss-prow]

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