PostgreSQL equivalent of mysqld --bootstrap or mysqld --init-file
You probably want the single user mode: --single, as described in the documentation:


  When invoked in single-user mode from the shell, the user can enter
  queries and the results will be printed to the screen, but in a form
  that is more useful for developers than end users. In the single-user
  mode, the session user will be set to the user with ID 1, and implicit
  superuser powers are granted to this user. This user does not actually
  have to exist, so the single-user mode can be used to manually recover
  from certain kinds of accidental damage to the system catalogs


Note that initdb has be run to initialize an empty data directory before creating databases or users. That would be the equivalent of mysql_install_db if you prefer to look at  this from the MySQL analogy angle.