API: Change calculation endpoints from POST to GET

[tahini]

These calculations are idempotent requests and do not trigger updates on the server. Therefore they correspond more to the definition of a GET request (see https://www.w3schools.com/tags/ref_httpmethods.asp)

GET also have the advantage to be easier to use and manage.

But in the parameters, we have geojson attributes for the origins and destinations. As get parameters, they should be changed to simply the coordinates of the points instead.

All requests with calculations are affected by this issue. As of today, they are accessibility, route and summary.

While these requests can be added to the current API, the current POST ones should be deprecated and we may want to increment the API version.