Support for Shared Google Drives

### Is your feature request related to a problem? Please describe.
Similar to #867 we also want to share the bookmarks file via Google Drive with our Team. Currently this does not seem possible and i am also unable to enter a Path besides the Root Folder. This always fails with a `c.files is undefined` error. We use a Shared Drive for all things that should be shared with the team and this would also be the best location to put the bookmarks file in.

### Describe the solution you'd like
Let me choose a Shared Drive which i have access to for syncing the bookmarks file.

### Describe alternatives you've considered
We are currently using Webdav but want to use Google Drive as this is more common among our users.

Start by locating the Google Drive sync implementation and tracing the `c.files is undefined` failure when a non-root path is entered. Compare the current root-folder flow with Shared Drive selection, then verify completion by syncing the bookmarks file from a team Shared Drive; the issue names no test or file to run.

Written by the indexing model from the issue text.