Deprecation of php7.2

[ChristophWurst]

Similar to #15079, php7.2 will only receive security fixes now and that will also end by the end of this year. We should plan ahead to smoothen the deprecation path. 19 will definitely support 7.2, though.

Ref #15079

cc @blizzz @nickvergessen @rullzer

[nickvergessen]

for 19 yes, 20 I'd say we should check where we are when it happens

[ChristophWurst]

Guess we should re-evaluate for 21. 7.2 will reach its EOL before the release of 21, ref https://www.php.net/supported-versions.php and https://github.com/nextcloud/server/wiki/Maintenance-and-Release-Schedule

[rullzer]

Yes 7.2 should die for 21
And we should have a look at support for 8

[ChristophWurst]

Done with #22767