[API] provide mock api response for /snapshots

[jeff-knurek]

Problem

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

This data is for DSL_ID 1 with a date range from 2020-08-18 to 2020-08-24 & 2020-09-18 to 2020-09-24

Proposed solution

• Create a controller for the API to respond to requests to /snapshots/{dsl id}/{DateStart}/{DateEnd}
• if the api request is /snapshots/1/1597708800/1598227200 then the hardcoded mock data with August data and NOT September data should be returned
• if the api request uses 2 as DSL id, then no data should be returned
• if the api request is not GET, or for other parameters, the response should be an error state