App Platform: How to set specific NodeJS version?

NodeJS projects have an optional configuration in their package.json for indicating the supported engine(s) for an app. This can look like:

{ 
  "engines" : { 
    "node" : "12.19.0" 
  }
}

ranges are also supported, for example:

{ 
  "engines" : { 
    "node" : ">=12.0.0 <=14.0.0" 
  }
}

this range says an app can be run on NodeJS 12 to 14 (inclusively).