Redesign interface of configPatch in plugin configurations

[randmonkey]

Is there an existing issue for this?

• I have searched the existing issues

Does this enhancement require public documentation?

• I have added an Acceptance Criteria item for adding and/or adjusting public documentation (if applicable)

Problem Statement

Continuing of #5687.
The current interface of configPatches in KongPlugin and KongClusterPlugin accepts raw JSON value in the value field. This format requires string values in the secrets to be quoted in double quotation marks, so the secrets have to be defined like

apiVersion: v1
kind: Secret
metadata:
  name: rate-limit-redis
stringData:
  password: '\"PASSWORD\"' 
type: Opaque

This is not user friendly. We need to define a more user friendly interface to let users to use configPatches easier.

Proposed Solution

• Redesign the user interface of configPatches in KongPlugins and KongClusterPlugins to make unquoted strings in secrets to be parsed and filled into Kong plugins' config correctly
• Make the interface to break existing interface in the least amount.

Additional information

No response

Acceptance Criteria

• Users can refer values in unquoted string format in secrets in configPatches of KongPlugin and KongClusterPlugin
• Do not break the existing interface if possible
• The guide page in the document is updated to include how to refer to values stored in secrets in Kong plugin config by configPatches