Kong Identity: Multiple active secrets for clients via Konnect and DCR

## Jobs to be done (optional)
When this feature is released customers can define multiple secrets against a client ID to facilitate credential rotation using both the Konnect Admin API and the DCR endpoint.

## Definition of done
Document how to rotate a credential in the UI and API (draft of request body needed from eng)

## Information
DRP: Andrew J.
Aha: https://konghq.aha.io/features/KID-21

## Due date (optional)

## Size
M

Start by locating the existing documentation for credential management in the UI, Konnect Admin API, and DCR endpoint. Request the draft API request body from engineering, then document the credential-rotation flow in both the UI and API; the issue is done when both paths are covered.

Written by the indexing model from the issue text.