Use activerecord_sane_schema_dumper

What does this MR do?

ActiveRecord::SaneSchemaDumper modifies the behavior of Rails’ ActiveRecord::SchemaDumper so that the generated db/schema.rb file doesn’t contain any useless/harmful whitespace column alignment.

Why was this MR needed?

To reduce potential conflicts in db/schema.rb (see https://gitlab.com/gitlab-org/gitlab-ee/issues/715).