How do I Install a vscode plugin in Theia directly from a git repo?

Question

I would like to install a VScode plugin in Theia. It works when I install by specifying the download location of the VSixPackage. Snippet of the package.json file:

.....
"scripts": {
    "postinstall": "download-debug-adapters"
},
"adapterDir": "plugins",
"adapters": {
    "vscode-cortex-debug": "https://marus25.gallery.vsassets.io/_apis/public/gallery/publisher/marus25/extension/Cortex-Debug/0.3.1/assetbyname/Microsoft.VisualStudio.Services.VSIXPackage"
},
.....

There is a fork of the extension that has some features I require. How do I install a VSCode extension directly from a git repo, eg.: https://github.com/Marus/cortex-debug