Feature: add transport information (and associated filters) to routes

**Community discussion about this feature (mandatory)**
Link to where this feature has been validated

**Expected behaviour**
When creating the route
- It must be possible to select starting points and ending points (which have to be access waypoints) in the route configuration section, just after selecting the route type. They are automaticaly estimated by the following algorithm:
- If the route is of type `return_same_way`, `loop_hut` and only one access waypoint is associated, this point is the starting point. No need to have an ending point in this case
- If the route is of type `loop`, all access waypoints are starting points. No need to have an ending point in this case
- If the route is of type `traverse`, `raid`, `expedition` and at least 2 access waypoints are associated, the 2 farthest access waypoints are considered as starting and ending waypoints
- Based on these points, a `public_transportation_rating` of the route is computed using the worst value bewteen :
- the best accessibility value of all starting points, and
- the best accessibility value of all the ending point (if they exists)

This algorithm may be applied to already existing routes, but it may require human checks to ensure data quality

When viewing a route
- A [public transport logo](https://fontawesome.com/icons/bus?f=classic&s=solid) 🚍 has to be dislayed on associated waypoints accessible by public transports
- A [play](https://fontawesome.com/icons/play?f=classic&s=solid) ▶ logo has to be dislayed on starting waypoints
- A [stop](https://fontawesome.com/icons/stop?f=classic&s=solid) ⏹ logo has to be displayed on ending waypoints
- The `public_transportation_rating` of the route has to be displayed in the route header

When searching for an access waypoints
- The `public_transportation_rating` filter must be a slider (instead of values selection: it's easier and quicker)

When updating an access waypoint
- The `public_transportation_rating` value of all the routes associated to the waypoint must be updated if this value has changed

When searching for a route:
- It must be possible to filter routes with a `public_transportation_rating` filter (also a slider, as for waypoints)

**Alternatives considered**
- A `public_transportation_access` information (a checkbox for instance) provided manually when creating the route, in order to certify that this route is accessible by public transportation. IMHO, this information has to be provided by the access waypoint information ; in this way the information is only provided at one time/place, and all the route linked to this waypoint are updated when the waypoint is. Inconvenient: it requires existing and updated access waypoints, or it needs waypoints creation apart from route creation
- A `soft_mobility_outings` information on the route header (yes/no if at least one outing has been associated to this route or outings associated to this route number). I don't know if it's relevant in this issue
- A `public_transportation_access` or `soft_mobility` checkbox route filter : easier and quicker than a slider, but allow less filter possiblity