Add robots.txt for non-production environment.

[v2nek]

User Story

As anyone, i want to have robots.txt for non-production environments to avoid penalty from search engines for exposing content and removing it without redirects.

Description

Type: Feature

Summary: Need to introduce /robots.txt location if environment is not production more details here: http://www.robotstxt.org/robotstxt.html env could be detected from env/config variable, we can introduce new one, or rely on existing.

Expected behavior

comment: # if you open https://develop.openbounty.status.im/robots.txt (replace develop with PR-number of your PR) it should display User-agent: * Disallow: /

for production environment it should be 404.

Actual behavior

comment: # 404 error on all environments.