Open workspace with files from a template context but no git remote

This is a revival of https://github.com/gitpod-io/gitpod/issues/86

Description

We would like to support opening archive URLs with Gitpod, e.g. like so:

https://gitpod.io/#https://github.com/gitpod-io/gitpod/archive/refs/heads/main.zip

This should give you a workspace containing all the files/directories from that archive, but no Git repository yet (i.e. no git init -- repository creation can then be done in a second step)

Use cases

• Allowing users to start new projects based on templates (e.g. one of https://www.gitpod.io/docs/quickstart, or a GitLab/Bitbucket template repository, or a ZIP file generated on https://start.spring.io/)

Alternatives

• Opening regular repositories in Gitpod, e.g. any one from https://www.gitpod.io/docs/quickstart; or some public repository; or a personal or private repository. This allows you to push changes if you already have access, or to create a fork if you don't have access, but creating brand new projects is inconvenient (you have to start by creating a repository yourself outside of Gitpod, as opposed to just starting to code in Gitpod and figuring out repo creation later on)
• Another idea to allow starting from templates would be to make Gitpod create and initialize a new repository for you. This was initialliy proposed here: https://github.com/gitpod-io/gitpod/issues/5583

No implementation files or tests are named. Start by tracing how Gitpod handles the example archive URL, then verify that the resulting workspace contains the archive files without a Git repository or remote. Done means archive-based workspace creation works while regular repository opening remains unaffected.