Feature request: make network settings lockable

[man-schu]

Describe the bug
The network settings can be changed by users. However, in a professional environment, this might be a setting that should only be changed by IT administrators.

To Reproduce
Steps to reproduce the behavior:

1. Go to 'Preferences'
2. Click on 'Network'

Expected behavior
I would expect that network settings can only be set by the computer administrator. There are different ways to make that possible, like for instance:

1. Network settings can only be changed when being a computer administrator.
2. Network settings are to be set in an configuration file which can be made read-only or which are only accessible by computer administrators.

Windows
• Windows Version: Windows 10
• Workrave Version: latest

Additional context
The request is especially interesting for companies with strict security rules. If this feature request is being taken into account it could boost the use of Workrave and thus attract more open source developers who are willing to contribute.