Fixes #19729: Secret variable engine

[ElaadF]

https://issues.rudder.io/issues/19729

⚠️ This part have been moved in https://github.com/Normation/rudder-plugins-private/pull/190

How to test it

1. Install secret-management plugin or create /var/rudder/configuration-repository/secrets/secrets.json with this content :

{
  "formatVersion" : "1.0",
  "secrets":[
      {
          "name" : "password",
          "description":"#markdown supported",
          "value" : "password-remplaced-yeeeah"
      }
  ]
}

2. Create a secret (or skip it if you create manually the file previously)
   
3. Create a node property testengine with a recognized format, like this :

{
  "login": "admin",
  "password": {
    "value": "${engine.secret[password]}"
  }
}

4. Create a technique using this node property (I used File content with ${node.properties[testengine][password]} as lines parameter)
5. Apply this technique through directives
6. Check if the interpolation worked

---

Todo

• Move this part in rudder-plugins-private

[ElaadF]

PR updated with a new commit

[ElaadF]

PR updated with a new commit

[ElaadF]

PR updated with a new commit

[ElaadF]

PR updated with a new commit

[ElaadF]

PR rebased

[ElaadF]

Commit modified

[VinceMacBuche]

I do think this should be in the plugin the property engine should be added dinamically, not hardcoded within Rudder

[ElaadF]

This code habe been moved in https://github.com/Normation/rudder-plugins-private/pull/190