Repository Container: Offer to create devcontainer.json when it does not exist

[chrmarti]

#1515

Using a repository that does not have a devcontainer.json ends with an error dialog. It would be great if we instead offered to create the devcontainer.json with the QuickPick sequence we already have. (E.g., use 'microsoft/python-sample-vscode-flask-tutorial').

[chrmarti]

Variations to this could be:

• Associate a local devcontainer.json instead of copying the definition into the project folder to avoid polluting the repository.
• Associate a local DevContainer definition that is readonly (and updates with updates to the Remote-Containers extension).

[egamma]

Support to add a dev container configuration when it doesn't exist has been added.

I've extracted the ideas from #1570 (comment) into a separate issue.

To verify:

• Run Remote Containers: Open Repository in Container...
• Enter a repository that does not have a dev container configuration, e.g. https://github.com/microsoft/vscode-npm-scripts.git

You will prompted with the dev container definitions quick pick.

[egamma]

To verify:

• Use 'Remote Containers: Open Repository in Container...' e.g. https://github.com/Microsoft/vscode-npm-scripts to clone a GitHub repository without a dev container configuration in a dev container
• You will be prompted to add a configuration

There is a bug on Window that was fixed in the latest. To verify you need extension version > 0.109