Support multi-root workspaces

It looks like this extension doesn't support multi-root branches. By experiment I noticed that at the moment it takes the first folder found in the workspace. (The first entry in the folder-array in the workspace-json)

It would be a nice edition to support having multiple roots showing in the sidebar or have the sidebar showing a selected root. (either one selected by the user or in some way automatically selected)

I have multiple roots in the same workspace and not all of them is to a GitLab server.