feat(layout): add Gallium-NL layout (@ririshi) (#7029)

### Description
I recently created a modded version of Gallium that is more suited for
typing a mix of English and Dutch, rather than just being optimized for
English. I'd love to start learning the layout, so having a visual guide
would be very useful. I think others in my situation (who type a mix of
English and Dutch) could also benefit from having this layout added.
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### Checks

- [x] Adding a layout?
- [x] Make sure to follow the [layouts
documentation](https://github.com/monkeytypegame/monkeytype/blob/master/docs/LAYOUTS.md)
  - [x] Add layout to `packages/schemas/src/layouts.ts`
  - [x] Add layout json file to `frontend/static/layouts` 

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frontend/static/layouts/gallium_nl.json

@@ -0,0 +1,62 @@
+{
+  "keymapShowTopRow": false,
+  "type": "ansi",
+  "keys": {
+    "row1": [
+      ["`", "~"],
+      ["1", "!"],
+      ["2", "@"],
+      ["3", "#"],
+      ["4", "$"],
+      ["5", "%"],
+      ["6", "^"],
+      ["7", "&"],
+      ["8", "*"],
+      ["9", "("],
+      ["0", ")"],
+      ["-", "_"],
+      ["=", "+"]
+    ],
+    "row2": [
+      ["b", "B"],
+      ["l", "L"],
+      ["d", "D"],
+      ["c", "C"],
+      ["v", "V"],
+      ["y", "Y"],
+      ["p", "P"],
+      ["u", "U"],
+      ["o", "O"],
+      [",", "<"],
+      ["[", "{"],
+      ["]", "}"],
+      ["\\", "|"]
+    ],
+    "row3": [
+      ["n", "N"],
+      ["r", "R"],
+      ["t", "T"],
+      ["s", "S"],
+      ["w", "W"],
+      ["f", "F"],
+      ["h", "H"],
+      ["e", "E"],
+      ["a", "A"],
+      ["i", "I"],
+      ["/", "?"]
+    ],
+    "row4": [
+      ["x", "X"],
+      ["q", "Q"],
+      ["m", "M"],
+      ["g", "G"],
+      ["j", "J"],
+      ["z", "Z"],
+      ["k", "K"],
+      ["'", "\""],
+      [";", ":"],
+      [".", ">"]
+    ],
+    "row5": [[" "]]
+  }
+}

packages/schemas/src/layouts.ts

@@ -155,6 +155,7 @@ export const LayoutNameSchema = z.enum(
     "gallium_angle",
     "gallium_v2",
     "gallium_v2_matrix",
+    "gallium_nl",
     "maya",
     "gallaya_angle_ansi",
     "gallaya_angle_iso",