[Enhancement] Global custom actions + Option to not wait for custom action to finish

[Doodeletion]

I'd like to propose 2 enhancements to custom actions.

If I understand correctly, custom actions currently can only be configured per reposity. It would be nice if it was possible to configure global custom actions that are available in all repositories. Maybe also custom actions for workspaces.

When running a custom action, SourceGit waits until the called program exits. It would be nice if there was an option when configuring a custom action to not have SourceGit wait. This would be useful for setting up custom actions that open a terminal and run a command with output you want to read (e.g. custom action that runs git status in your terminal). Right now you can not continue using SourceGit until you closed the terminal that was opened by the action.

[Doodeletion]

I'd be willing to try and implement this, if this suggestion is accepted. I'm new to Avalonia but I have some experience with WPF.

[love-linger]

Done. You can download the latest CI build from Github Action.

[Doodeletion]

Thanks, just played around with it on windows, works great.

What do you think about adding global custom actions to the application preferences settings?