Support for custom commands like `:G` for opening the source control panel

Is your feature request related to a problem? Please describe.
I want to be able to add custom commands to command mode : , so I can mimic Vim plugin behaviors using native VSCode actions.

Describe the solution you'd like
Probably in the same way we remap keybindings, we could have a setting key like customCommands that would receive a list of command names => action to execute

Describe alternatives you've considered
I could use VSCode’s default Cmd + Shift + G, or map it to something like <leader>G, however, it would be good to register commands like :G (vim fugitive).
And then, since it is a custom table, it would be up to the users to map all commands they want:

"vim.customCommands": {
  "G": "workbench.view.scm",
  "Git": "workbench.view.scm",
  "G push": "git.push",
  "Git push": "git.push",
}

No files, tests, or entry points are named. Start by locating the command-mode parser and the extension's settings and VS Code action-registration paths, then determine how a custom command mapping would be represented and invoked; done means documented custom command settings work for the requested examples without breaking existing command mode.