[API] provide mock api response for /environments

[jeff-knurek]

Problem

the frontend has already created a mock api response for the /environments endpoint: https://github.com/TheIOFoundation/ProjectLockdown/blob/master/MAP/public/data/environment.response.json

This data is for DSL_ID 1.

Proposed solution

• Create a controller for the API to respond to requests to /environments/{dsl id}
• if the api request is /environments/1 then the hardcoded mock data should be returned
• if the api request is /environments/2 then no data should be returned
• if the api request is not GET, or for other parameters, the response should be an error state