💡 Feature Request: Fallback to isomorphic-git when git is not installed on the client

[jasikpark]

It would be helpful if degit supported being run in clients that don't have git installed, for example, https://stackblitz.com and other browser-based dev environments -- would it be possible to fall back on https://isomorphic-git.org/en when we detect the client not having git installed locally? That would be helpful for our usecase working on create-astro, which uses degit to clone our default templates or a template supplied by the user.

(https://github.com/petersalomonsen/wasm-git also exists, but seems less developed.)