[Bug]: cancel dbus activation for unconfigured clients on linux

### ⚠️ Before submitting, please verify the following: ⚠️

- [X] This is a **bug**, not a question or a configuration issue.
- [X] This issue is **not** already reported on Github (I've searched it).
- [X] Nextcloud Server and Desktop Client are **up to date**. See [Server Maintenance and Release Schedule](https://github.com/nextcloud/server/wiki/Maintenance-and-Release-Schedule) and [Desktop Releases](https://nextcloud.com/install/#install-clients) for supported versions.
- [X] I agree to follow Nextcloud's [Code of Conduct](https://nextcloud.com/contribute/code-of-conduct/)

### Bug description

Nextcloud is now always dbus-activated in GTK-environments (see: https://github.com/nextcloud/desktop/pull/6031). That means it starts itself on filesystem access. This is fine by itself.
Whats problematic about it is that it also starts up if it's *only is installed, not configured* on every login and presenting the "login screen". This is a huge problem for multi-user-systems, where only 1 user needs nextcloud. As this currently cant turned off.

### Steps to reproduce

1. Have Nextcloud installed
2. Login to the PC user account

### Expected behavior

On dbus-activation, Nextcloud client should check if its configured and end itself again without showing a window if not.

### Which files are affected by this bug

No files are involved.

### Operating system

Linux

### Which version of the operating system you are running.

ArchLinux, Ubuntu, Fedora

### Package

Distro package manager

### Nextcloud Server version

27.1.5

### Nextcloud Desktop Client version

3.11.0

### Is this bug present after an update or on a fresh install?

Fresh desktop client install

### Are you using the Nextcloud Server Encryption module?

Encryption is Disabled

### Are you using an external user-backend?

- [ ] Default internal user-backend
- [ ] LDAP/ Active Directory
- [ ] SSO - SAML
- [ ] Other

### Nextcloud Server logs

```shell
Arch Upstream mentioning: https://gitlab.archlinux.org/archlinux/packaging/packages/nextcloud-client/-/issues/2#note_158751
```

### Additional info

_No response_

No source files are named in the report. Reproduce the login behavior on a Linux installation and trace the desktop client's D-Bus activation and startup path, checking how an unconfigured client is detected. Done means an unconfigured client exits without showing a login window while configured clients continue to start normally.

Written by the indexing model from the issue text.