feature: Support boolean parameter or that a string parameter is converted into a boolean

[cmoulliard]

Feature request

Support boolean parameter or that a string parameter is converted into a boolean. Ideally we should have a collection of functions able to perform $(params.PRIVILEGED | toBoolean)

Use case

Tekton don't propose a way to define a boolean parameter or to convert a string parameter to a boolean as this is needed to configure the following field: pod > securityContext > privileged: true

The only working solution implied to duplicate the code of the task which is a bit boring and to use when

Example:

apiVersion: tekton.dev/v1
kind: PipelineRun
metadata:
  name: pr-echo
spec:
  params:
    - name: HELLO
      value: "Hello World!"
    - name: BYE
      value: "Bye World!"
    - name: PRIVILEGED
      value: false
  pipelineSpec:
    tasks:
      - name: echo-privileged-true
        when:
          - input: "$(params.PRIVILEGED)"
            operator: in
            values: [ "true" ]
        taskSpec:
          steps:
            - name: echo-privileged-true
              image: ubuntu
              script: |
                #!/usr/bin/env bash
                
                echo "The value of the param PRIVILEGED is: $(params.PRIVILEGED)"
                echo "$(params.HELLO)"
              securityContext:
                privileged: true

      - name: echo-privileged-false
        when:
          - input: "$(params.PRIVILEGED)"
            operator: in
            values: [ "false" ]
        taskSpec:
          steps:
            - name: echo-privileged-false
              image: ubuntu
              script: |
                #!/usr/bin/env bash
                
                echo "The value of the param PRIVILEGED is: $(params.PRIVILEGED)"
                echo "$(params.HELLO)"
              securityContext:
                privileged: false