Persist folders added to project (save workspace)

[redoxeon]

Is your feature request related to a problem? Please describe.
I'd like to be able to open multiple folders in a single project or workspace without having to add individual folders every time I open Zed.

Describe the solution you'd like
Something similar to VS Code's "Save workspace" feature where you can have a set of folders (and potentially settings) saved as a workspace/project.

Describe alternatives you've considered
Current alternatives involve opening one folder, then the others in succession through "add folder to project" or to put all project folders in a "super-folder" that can just have all sub-projects in it.

[mikayla-maki]

Blocks on: https://github.com/zed-industries/feedback/issues/430

[mikayla-maki]

This should ship in a few releases