This changes the way launchagents are installed via `.pkg` files.
The installers are updated to no longer use `launchtctl load` but rely on `launchctl bootstrap` instead to load in the current user context.
For the Agent, this fixes a problem where the installer would initially start in a root context.
For the GUI package this changes to not rely on `open` to start Duplicati, as that appears to be incompatible with `bootstrap`
The uninstallers are updated handle both `load` / `unload` and `bootstrap` / `bootout` before removing the launchagents.
This fixes#5766
