[Enhancement] Please clarify the use of double curly braces for jmesPath in external variables

[jsalatiel]

Description

It would be really nice if the docs could clearly explain the difference/possibility of using double curly braces in jmespath for external variables.
I tried to create a policy that would set a variable based in one optional annotation or fallback to another annotation ( mandatory ) , in this case prefixed by some path.

The only way that worked ( thanks to @realshuting ) was to mix part of the request without double curly brace and part of it with double curly brace like this.

    - name: mountpath
      variable:
        jmesPath: request.object.metadata.annotations.optional || '/etc/ssl/{{request.object.metadata.annotations.mandatory"}}'

It would be nice to have a better understanding of that in the docs. Is that only for concatenation? What else?

Thanks!

Slack discussion

https://kubernetes.slack.com/archives/CLGR9BJU9/p1728944204996649

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[realshuting]

Adding working samples, playground.

[realshuting]

By default for a plain JMESPath variable, no double curly brackets are needed in variable.jmesPath, for example:

    - name: mountpath
      variable:
        jmesPath: request.object.metadata.annotations.optional

Nested variables need to be wrapped with {{}}, for example:

    - name: mountpath
      variable:
        jmesPath: request.object.metadata.annotations.optional || '/custom/string/{{request.object.metadata.annotations.mandatory"}}'

[A-5ingh]

/assign