Conditional execution of steps with if

[drevell]

TL;DR

We could add the ability to conditionally execute one or more template steps using a CEL predicate.

• @verbanicm

Detailed design

There are two possibilities we can think of for how this might work. There could be an `if` field on every action, or there could be a new action type `if`.

Design 1: an `if` field on every action


inputs:
  - name: 'include_auth0'

steps:
  - action: 'include'
    if: 'bool(include_auth0)'
    desc: 'conditionally include auth0 integration'
    params: 
      paths: ['auth0']

Design 2: a new action type for if that has a list of steps:

inputs:
  - name: 'include_auth0'

steps:
 - action: `if`
   params:
     then:
       - action: 'include'
          expr: 'bool(include_auth0)'
          desc: 'conditionally include auth0 integration'
          params: 
            paths: ['auth0']

### Alternatives considered

_No response_

### Additional information

_No response_