Have a script that can check for (github) release updates for community-scripts LXCs

[burgerga]

Many scripts check the latest release version from github and then compare this to /opt/{$APP}_version.txt.
I think it would be nice if you could check if there are update to your LXCs from the proxmox shell, to give you an output like this (completely made up):

$ check_community_scripts_updates
adguard (102): 1.0.2 -> 1.1.0
mealie (103): 2.0.0 (up-to-date)
madeupapp (141): 3.0.1 (not updateable)
madeupapp2 (151): 4.9.5 (update check not supported yet)
linkwarden (160): 2.0.0 -> 3.0.0
...

A possible way to do this, would be to split the current update function into two, where the new function update_check (or something) only handles the version comparison, which would then by used in the update function to do the actual update. That way:

• update keeps working like it works now
• the feature can be added to apps over time during a refactor/update
• Checking the existence of update and update_check can be used to inform user if this is supported (see example above)
• Could also work for non-github apps, then you will have a different update_check function

Completely open to different approaches as well, this was the 2nd second thought that came to mind.
My first thought was having a github repo link stored in some sort of json (like for the frontend information), but this will be more overhead. An advantage of this could be that you could do the latest release check using a github action, and then use this as cache for the update_check function, to avoid hammering the github API.