Combine multiple projects with the same annotation labeling interface

**Is your feature request related to a problem? Please describe.**
I annotated 2 groups of images, each group in a different project. I want to combine the two projects, how do I do that? The documentation to import predictions or annotations are not that clear.

**Describe the solution you'd like**
For example an option to copy one (or multiple) task (image + annotation) from one project to another

**Describe alternatives you've considered**
An alternative will be a manual local aggregation of the json files of the both projects and re upload that to Label studio. The problem here I don't know how to upload this json as a project.

**Additional context**
None