Customize Add Docker Files To Workspace

[conradwt]

Goal

I would like to be able to add additional languages as well as customize existing languages for my development workflows without having to submit a PR to update the extension.

Currently

The supported languages are fixed and new customizations need to be redeployed within a future version of this extension.

Possible Solution

Extend the extension to allow users to add their own templates to a designated directory that would get picked up and displayed within VS Code when one uses Docker Add command.

[bwateratmsft]

I think this is basically what #1617 is about, so I'll mark this one as a dupe of that. I did update the issue text there to include your additional suggestions.