Simplify Integration#api_field_names after security fix

The following discussion from https://gitlab.com/gitlab-org/security/gitlab/-/merge_requests/2369 should be addressed:

• @.luke started a discussion: (+1 comment)

  Thought

  After this change merges to master, in a follow-up, it should be possible change Integration#api_field_names to:

  def api_field_names
    fields.reject { _1[:type] == 'password' }.pluck(:name)
  end

  What do you think?

Availability & Testing

We have tests around this behavior at the unit and request layer

These tests should be great to support this effort, and assert that no sensitive fields will leak through.