check_os_updates improvement

[Saevar2000]

Can you add logic to check_os_updates (or maybe create a new one check_os_eol?) that detects when OS end-of-life date is and return warning/critical with message when the end-of-life date is if it is in x many days.

https://endoflife.date/docs/api has all the end-of-life dates needed. What do you think?

[sni]

Sounds helpful, would you want to take a look at that check?

[Saevar2000]

I can make an attempt (I have never programmed in go before), if you don't have time for it.