This is the complete answer (GitBash + color scheme + icon + context menu)
- Set default profile:
"globals": 
{
    "defaultProfile" : "{00000000-0000-0000-0000-000000000001}",
    ...
- Add GitBash profile
"profiles": [
    {
        "guid": "{00000000-0000-0000-0000-000000000001}",
        "acrylicOpacity": 0.75,
        "closeOnExit": true,
        "colorScheme": "GitBash",
        "commandline": "\"%PROGRAMFILES%\\Git\\usr\\bin\\bash.exe\" --login -i",
        "cursorColor": "#FFFFFF",
        "cursorShape": "bar",
        "fontFace": "Consolas",
        "fontSize": 10,
        "historySize": 9001,
        "icon": "%PROGRAMFILES%\\Git\\mingw64\\share\\git\\git-for-windows.ico",
        "name": "GitBash",
        "padding": "0, 0, 0, 0",
        "snapOnInput": true,
        "startingDirectory": "%USERPROFILE%",
        "useAcrylic": false
    }
]
- Add GitBash color scheme
  "schemes": [
      {
          "background": "#000000",
          "black": "#0C0C0C",
          "blue": "#6060ff",
          "brightBlack": "#767676",
          "brightBlue": "#3B78FF",
          "brightCyan": "#61D6D6",
          "brightGreen": "#16C60C",
          "brightPurple": "#B4009E",
          "brightRed": "#E74856",
          "brightWhite": "#F2F2F2",
          "brightYellow": "#F9F1A5",
          "cyan": "#3A96DD",
          "foreground": "#bfbfbf",
          "green": "#00a400",
          "name": "GitBash",
          "purple": "#bf00bf",
          "red": "#bf0000",
          "white": "#ffffff",
          "yellow": "#bfbf00",
          "grey": "#bfbfbf"
      }
  ]
- To add a right-click context menu "Windows Terminal Here"
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\Directory\Background\shell\wt]
@="Windows terminal here"
"Icon"="C:\\Users\\{YOUR_WINDOWS_USERNAME}\\AppData\\Local\\Microsoft\\WindowsApps\\{YOUR_ICONS_FOLDER}\\icon.ico"
[HKEY_CLASSES_ROOT\Directory\Background\shell\wt\command]
@="\"C:\\Users\\{YOUR_WINDOWS_USERNAME}\\AppData\\Local\\Microsoft\\WindowsApps\\wt.exe\""
- Replace {YOUR_WINDOWS_USERNAME}with your Windows username.
- Create an icon folder, put the icon there and replace {YOUR_ICONS_FOLDER}with your icon folder.
- Save this in a .regfile and run it.