Support list as model constants

[jijn]

• Please check if the PR fulfills these requirements

• The PR follows our guidelines (formatting & style)
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  feature, related to Add strings & lists to model constants #1010

• What is the current behavior? (You can also link to an open issue here)
  support double, int, bool, string, tensors...

• What is the new behavior (if this is a feature change)?
  support list

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
  no

• Other information:

set Model constant l = (3,1,4,1,5,9,2), list

or

set Model constant l = 3,1,4,1,5,9,2, list

[fractalsbyx]

I think if we want to do lists, we would have keywords like STRING LIST, INT LIST, BOOL LIST, etc.
(skipping tensors and anything complicated)

[landinjm]

With #1110 it might be better to close and remake this PR