robots.txt files for draft.ocw.mit.edu, live-qa and draft-qa servers

[pdpinch]

User Story

Users don't want to get search results from google for live-qa.ocw.mit.edu or any of the other qa and draft servers

Acceptance Criteria

• [ ] Don't break the robots.txt file for https://ocw.mit.edu
• [ ] Write a github action to test the contents of https://ocw.mit.edu/robots.txt -- it should always include Allow: / and Sitemap: https://ocw.mit.edu/sitemap.xml
• [ ] https://live-qa.ocw.mit.edu/robots.txt should be set to deny all
• [ ] https://draft-qa.ocw.mit.edu/robots.txt should be set to deny all
• [ ] https://draft.ocw.mit.edu/robots.txt should be set to deny all (currently it returns a 503 error)