Switch clients version to download on Enrollment

[teon]

Client request:

Make it possible to override the version tag where the download links point to, per individual OS type
This would be useful when defguard fixes issues and releases and alpha version

For example, now we point our Linux users to the 1.6.0-testbuild2 version, so they don't need to set the timeout to a couple hours, due to the stats/disconnect issue we encountered.

@Va1ter I think best would be to add a setting for the Enrollment component and then choose a channel for an operating system, eg.:

• Windows: stable/testing
• Linux: stable/testing
• macOS: stable/testing