Add dynamic Map route

[PalAditya]

For now, when the map preview shows up, it only shows the marker to destination. We need it to show the complete route from our location to destination.

Idea: Use directions API (https://maps.googleapis.com/maps/api/directions/json?origin={Start}&destination={End}&mode=driving&key=YOUR_API_KEY) to get the driving route (in result.overview_polyline.points ), which is encoded. The function to decode it is already in index.js, and you need to send a request to maps static API (http://maps.googleapis.com/maps/api/staticmap?sensor=false&zoom=16&size=400x400&path=The_decoded_path_from_above}&key=YOUR_API_KEY) to show the image on the Basic Card already there in dialogflow

Requirements: Synchronous operation is not allowed. Use Promises and asynchronous operation to chain the API calls and then return the results.

[apsknight]

@PalAditya Could you please add some screenshots of required feature by mimicking the behavior in native Google Assistant?

[PalAditya]

Sure. For a longer distance (say Kolkata-Bhubaneswar), the Google assistant shows:

For a shorter distance (say Khurdha-Bhubaneswar), we have:

We want to mimic this functionality accurately, with as many polylines (turns) as possible to get from the maps API.