postgresql: update to 12.1

[mustaqimM]

createlang and droplang has been deprecated since PostgreSQL 9.1

plctcl - Since createlang has been deprecated, CREATE EXTENSION {pltcl,pltclu} is needed to use it (I don't use this, so could someone please check if it's correct). See here

New versioning policy since PostgreSQL 10

PostgreSQL 12 release notes
PostgreSQL 11 release notes
PostgreSQL 10 release notes

Since more than 1 version has passed, pg_upgrade or pg_dumpall might be needed to be run on any DBs.

[Chocimier]

Upgrading with pg_upgrade requires to have binaries of both version installed at the same time, and updating with pg_dumpall require to dump database before uninstalling old version. Simply upgrading package will make exisiting databases unusable. I am working on separate packages installing version 12 aside, will push in-progress state soon.

[mustaqimM]

sorry, didn't see the PR, multiple versions would be the better method