0.13: [Bug]: Template variables are being interpolated on input values

[stefreak]

Garden Bonsai (0.13) Bug

Current Behavior

The action prints the literal text I shouldn't be here..

Expected behavior

I expect the action to print the literal text ${local.env.UNINVOLVED_VAR}

Reproducible example

Run UNINVOLVED_VAR="I shouldn't be here." INCONSPICUOUS_VAR='${local.env.UNINVOLVED_VAR}' garden run debug with this garden.yml:

apiVersion: garden.io/v1
kind: Project
name: foo

environments:
  - name: dev

providers: []

---
kind: Run
type: exec
name: debug
spec:
  command:
  - echo
  - '${local.env.INCONSPICUOUS_VAR}'

Workaround

None available

Suggested solution(s)

Parse templates into an abstract representation, and from there do not interpolate template strings anymore on any of the intermediate evaluation results.

Additional context

Unfinished, but this would fix this: #5496

Your environment

• OS: all

garden version Bonsai and Acorn affected.