output topo lines in ft

default top lines are in meters. update the object with "id": "contour-label" as follows

to-string(round(ele * 3.28084) & ' ft')

"layout": "text-field":

[
  "to-string",
  [
    "concat",
    [
      "round",
      [
        "*",
        ["get", "ele"],
        3.28084
      ]
    ],
    " ft"
  ]
]