Add list of Postgres extensions to extended Postgres image

Following extension were added

Timescale
Citus
PoWA extensions 
pg_timetable 
pg_show_plans 
pg_cron
postgresql_anonymizer 
pg_stat_kcache 
pg_qualstats 
bg_mon
pgextwlist
pg_auth_mon 
set_user

Moreover docker file were reworked to reduce image size. Now it adds 45Mb to base image:

postgres-extended-96  249MB
postgres-extended-10  250MB
postgres-extended-11  344MB
postgres-extended-12  359MB

Due to my oversight first 5 commits have been already merged to master.