[Feature Request] Allow stackfile to be set/modified based on UI env variables

[Codelica]

Is your feature request related to a problem? Please describe.
Nope...

Describe the solution you'd like
Currently Portainer stack templates (type=2 or 3) must supply a hardcoded url and stackfile to specify the correct stack file to include. In our case it would be great if the "stackfile" could be dynamically set based on a UI variable.

For example, we have to support 4 different platforms/environments for our stacks to run on, each of which requires a unique stack file for various differences (image arch, volumes, etc). Currently that means we need to create 4 different stack templates for Portainer, each pointed to their respective stackfile.

What would be great is if we could use one of the UI variables to set/modify that stackfile location. For example, we'd include an env variable like:

"env": [
      {
        "name": "EC_PLATFORM",
        "label": "Platform (IMPORTANT)",
        "select": [
          {
            "text": "QNAP Intel",
            "value": "qnap-intel",
            "default": true
          },
          {
            "text": "QNAP ARM",
            "value": "qnap-arm"
          },
          {
            "text": "Intel x86_64",
            "value": "intel"
          }...

and then potentially use it in some way like:

"stackfile": "v2/${EC_PLATFORM}/mt-mtweb-updates.yml"

Such that 1 app template could service multiple platforms/environments, which in our case would reduce the app template list by 3/4's.

Describe alternatives you've considered
Potentially the "stackfile" param could just allow for UI based variables directly just as the "env" section does currently. Off hand I'm not sure if that would entail more work or not though.

Additional context
Thanks for your work here... super helpful project :)

[mazmar]

Could this be extended to all json definition? I'd like to create a template for our mock server where container port is fixed and user should choose only host port

e.g
"ports": [
"{PORT}:80/tcp"
]