Move map generator into main repo (#2006)

## Description:

Move the MapGenerator repo into OpenFrontIO so we don't need to copy
generated map files over.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:

evan

map-generator/README.md

@@ -0,0 +1,33 @@
+# MapGenerator
+
+This is a tool to generate map files for OpenFront.
+
+## Installation
+
+1. Install go https://go.dev/doc/install
+2. Install dependencies: `go mod download`
+3. Run the generator: `go run .`
+
+## Creating a new map
+
+1. Create a new folder in assets/maps/<map_name>
+2. Create image.png
+3. Create info.json with name and countries
+4. Add the map name in main.go
+5. Run the generator: `go run .`
+6. Find the output folder at generated/maps/<map_name>
+
+## Create image.png
+
+1. Download world map (warning very large file) https://drive.google.com/file/d/1W2oMPj1L5zWRyPhh8LfmnY3_kve-FBR2/view?usp=sharing
+2. Crop the file (recommend Gimp), we recommend roughly 2 million pixels for performance reasons. Do not go over 4 million pixels.
+
+## Create info.json
+
+- Look at existing info.json for structure
+- Use country codes found here: https://en.wikipedia.org/wiki/List_of_ISO_3166_country_codes
+
+## Notes
+
+- Islands smaller than 30 tiles (pixels) are automatically removed by the script.
+- Bodies of water smaller than 200 tiles (pixels) are also removed.