Disable Rubocop for PostgreSQL patches

This code is mostly a copy-paste from existing pull requests so there's
no point in running Rubocop on it.

config/initializers/postgresql_opclasses_support.rb

+# rubocop:disable all
+
 # These changes add support for PostgreSQL operator classes when creating
 # indexes and dumping/loading schemas. Taken from Rails pull request
 # https://github.com/rails/rails/pull/19090.