Expose MAML layers targetCellType

[pomadchin]

Overview

This PR adds an optional configuration option to all MAML layers. If set than the result layer would be lazily interpreted as a layer with the given cellType.

Checklist

• Description of PR is in an appropriate section of the CHANGELOG and grouped with similar changes if possible

Demo

stac-lc8-rgb = {
  type = "mapalgebrasourceconf"
  name = "stac-lc8-rgb"
  title = "Landsat LayerUS RGB"
  target-cell-type = "int32raw" // or whatever supported by GeoTrellis
  // ...
}