fix: add missing maintainer field

[t-aleksander]

📖 Description

Added authors details to the cargo.toml file which is also used as the maintainer field in the resulting .deb package. Without the maintainer field, some apt commands would constantly display the following warning:

dpkg: warning: parsing file '/var/lib/dpkg/status' near line 3474 package 'defgu
ard-client':
 missing 'Maintainer' field

Let me know if I should change the author to something more informative.

fixes #204

Before:

> apt show ./defguard-client_0.3.0_amd64.deb
Package: defguard-client
Version: 0.3.0
Priority: optional
Maintainer:
...

After:

> apt show ./defguard-client_0.3.0_amd64.deb
Package: defguard-client
Version: 0.3.0
Priority: optional
Maintainer: Defguard
...

🛠️ Dev Branch Merge Checklist:

Documentation

• If testing requires changes in the environment or deployment, please update the documentation (https://defguard.gitbook.io) first and attach the link to the documentation section in this pool request
• I have commented on my code, particularly in hard-to-understand areas

Testing

• I have performed manual tests manually and all changes work
• New and existing unit tests pass locally with my changes

🏚️ Main Branch Merge Checklist:

Testing

• I have merged my changes before to dev and the dev checklist is done
• I have tested all functionalities on the dev instance and they work

Documentation

• I have made corresponding changes to the user & admin documentation and added new features documentation with screenshots for users/admins

[t-aleksander]

Also tested by installing the package. The warning doesn't show up anymore. Results of apt show defguard-client:

Package: defguard-client
Version: 0.3.0
Status: install ok installed
Priority: optional
Maintainer: Defguard
Installed-Size: 75.5 MB
Depends: libayatana-appindicator3-1, libwebkit2gtk-4.0-37, libgtk-3-0
Homepage: https://github.com/DefGuard/client
Download-Size: unknown
APT-Manual-Installed: yes
APT-Sources: /var/lib/dpkg/status
Description: (none)
 Defguard desktop client.