Fix workspace name when restoring a workspace

[fvalenza]

Hello and thanks for this plugin !

Currently when restoring a workspace, it restores the state (tabs/panes/processes) without restoring the workspace name ( hence we are still on default workspace and in the spawned window, no traces of the name of restored worspace)

This PR shall fix this:

• When opts.spawn_in_workspace is true -> add the restored workspace to the current instance of wezterm and switch to it
• When opts.spawn_in_workspace is false -> spawn a new instance with the restored workspace's state + rename it accordingly so we can continue editing the same workspace (instead of manually renaming it).

Fixes #114