Add option to skip checking for updates on startup

### I am planning on implementing this myself

No

### Describe your request

There is an existing option in the Mod Options menu called "Auto-update mods on startup", but Everest still checks for mod updates on startup and displays an alert on the main menu e.g. "Updates available for 3 mods".

I would like the ability to skip the update check entirely, meaning Everest does not make any internet calls at all.

### Additional context

_No response_