Animations for expeditions (Military Symbols)

[MiklerGM]

This issue is connected to #155 #94

In order to implement animations for expeditions or LineStrings we need to modify data set provided to mapbox on the fly. So we can't use MVT.
https://docs.mapbox.com/mapbox-gl-js/example/animate-a-line/

For this purpose I would propose to create a separate endpoint for serving full GeoJSON with every military symbol for specified narrative (not narration).

Second Problem -- additional research needed
The speed of animation will depend on number of points.
Straight line would be animated in one animation frame, triangle in three and so on.

To keep the animation speed steady the LineString should be populated with points with similar space in between

I've been looking into smooth functions, like https://postgis.net/docs/ST_ChaikinSmoothing.html
But I think they will have zero effect on a straight line