systemd unit ordering dependencies

### Feature Description

I noticed that DMS has a tray icon fix for if app icons don't appear in the system tray by generating an override. This in turn ensures DMS starts before the autostart apps.

The feature requested is to modify the current method of systemd ordering dependencies into one that will fix issues such as the need for a Tray Icon Override.

### Use Case

The advantage of this method is it then would apply to all users while also preventing the need for an override at all. Without the need for an override, the proposed change can be incorporated from the very beginning during DMS installation

### Compositor(s)

All compositors

### If Other, please specify

_No response_

### Proposed Solution

I believe there is a more appropriate fix rather than relying on an override that only applies to the current user, and that is changing the override which sets xdg-desktop-autostart to start after dms.service, to the proper method which should be setting dms.service to start after xdg-desktop-autostart.target.

### Alternatives/Existing Solutions

Here are a few examples of this implementation method done correctly

> rg xdg-desktop-autostart /usr/lib/systemd/user/

/usr/lib/systemd/user/plasma-workspace.target
16:Wants=xdg-desktop-autostart.target
19:Before=xdg-desktop-autostart.target

/usr/lib/systemd/user/ssh-agent.service
4:After=xdg-desktop-autostart.target
14:WantedBy=xdg-desktop-autostart.target

Inspect the user systemd unit for dms.service and the installation logic that creates or installs it. Compare its ordering with xdg-desktop-autostart.target and the examples under /usr/lib/systemd/user/. Done means DMS is ordered after the target for all users without requiring a per-user tray icon override.

Written by the indexing model from the issue text.