Vendored DAST template should use test stage

Summary

The Vendored DAST template merged in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9921 and to be shipped with %11.9 has its stage incorrectly set to dast when it should be set to test. It also includes predefined stages which can conflict with a user's.

Steps to reproduce

Include DAST.yml within a .gitlab-ci.yml and set a limited number of stages; i.e.

stages:
  - test

include:
  - template: DAST.gitlab-ci.yml

This results in the following error:

Status: syntax is incorrect
Error: dast job: stage parameter should be test 

What is the current bug behavior?

Cannot set DAST build stage within a CI config

What is the expected correct behavior?

A user can define the stage config for their DAST job.

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com

Possible fixes

Remove stages config from template and set stage: dast to stage: test