Support re-adding database source to workspace

[Marcono1234]

Is your feature request related to a problem? Please describe.
Currently when a database is imported, its source folder is automatically added to the workspace.
However, if you for some reason the source folder is not shown anymore (e.g. you manually removed it from workspace), then it appears there is no easy way to add it back.

Describe the solution you'd like
When right-clicking a database in the list of databases, the extension should check whether the source folder of this database is shown in the current workspace. If not, a context menu "Add database source folder to workspace" (or similar) should be offered.

Describe alternatives you've considered
Workaround:

1. Remove the database
2. Import it again