CentOS streams clarifications

A couple of clarifications where I fumbled versions and dates (give me a break I was only half a coffee deep and it was 6AM here).
RHEL8 release was may 2019 not 2018; I used this at the start of the spot, but life-cycle comments were correct in their span/dates in the rest of the segment.

Application streams currently don't ship the kernel as an appstream; but there is no reason it couldn't leverage it, just currently no reason to in the 8 release.

Postgres versions in the current RHEL8 app-stream are 9.6, 10, and 12. Stream 10 being the default in RHEL8. I used incorrect versions in an example I gave.

Chur & Happy New Year!
- Joel