Revert "config: Remove the topo50 gridless and topo250 layers. (#775)"

This reverts commit e8c2658.

config/tileset/topo.json

@@ -0,0 +1,21 @@
+{
+  "type": "raster",
+  "id": "ts_topo",
+  "title": "NZ Topo Map",
+  "description": "The Topo map provides topographic mapping for the New Zealand mainland and offshore islands at 1:50,000 scale.",
+  "background": "cee5f2ff",
+  "layers": [
+    {
+      "2193": "s3://linz-basemaps/2193/topo250_2020_21-17m/01ENS2R7PB3K2HPW1032ZXJKXD",
+      "name": "topo250_2020_21-17m",
+      "maxZoom": 13,
+      "title": "New Zealand Topo250 Map Series (2020)"
+    },
+    {
+      "2193": "s3://linz-basemaps/2193/topo50-gridless_2020_4-23m/01EFJ7EHQRJJ70XWBEJXGEAW6W",
+      "name": "topo50-gridless_2020_4-23m",
+      "minZoom": 14,
+      "title": "New Zealand Topo50 Gridless Map Series (2020)"
+    }
+  ]
+}