[Development] [HEADS UP] new branching scheme: 5.3 branches created, stable deprecated

[Oswald Buddenhagen]

hello,

we finally have CI setups for the new branching scheme. this means that
5.3 (and 1.0 in enginio) are now the target branches for stabilization
changes aimed at the 5.3.1 release.

the stable branches will continue to exist for the next weeks and will
be merged into 5.3/1.0 regularly, so you can finish and integrate your
pending reviews.

do *NOT* re-push your pending changes for/5.3.

however, do not push new reviews for/stable (this can't be technically
prevented without preventing amends to existing changes, so i'm leaving
it open for the time being).