[Feature request] - Theme update checker

[Rushaway]

Is your feature request related to a problem? Please describe.

Currently, authors of the theme can not notify these users if a new update is available

Describe the solution you'd like

An theme update checker, based on a link provided in the theme.conf Like for the current sourcebans https://sbpp.github.io/version.json

Describe alternatives you've considered

N/A

Additional context

The system is already present, it just need to be extended to theme.