[c-c create] make post-create step optional (closes #2712041) In this context the "post-create" step refers to the database's creation and initialization. We want to be able to create a new instance but skip the database creation (`db-create` and `db-init` commands) in automatic setup.

cubicweb-web: embedded-javascript-library usr/share/cubicweb/cubes/shared/data/jquery.js