feature: Document ways to run kcp with operator

[mjudeikis]

Feature Description

After recent changes kcp operator now supports few modes of running kcp:

1. Authentication at the edge and authorization at shards
2. Authentication and authorization at shards (passthrough on frontproxy).

Prs related to this:
#81
#78
#75
#74

Proposed Solution

We should document both modes and differences for them

Alternative Solutions

No response

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Additional Context

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