cubicweb-postgis #3098180 postgres: gis function with a "create_extension" file [validation pending]

Like with plpython and pglplsql.

prioritynormal
typeenhancement
done in0.4.0
load left0.000
closed by#964cb4e46cba Create extension postgis on db-create / add_cube (closes #3098180)
patchCreate extension postgis on db-create / add_cube (closes #3098180) [applied]