Add vector tile configuration, graph build improvements

[leonardehrenfried]

This makes the following changes:

• it enables the vector tiles API as requested by @slvlirnoff
• adds a workflow for running the graph build during a PR
• doesn't cache the OSM data download anymore since it would never update the cache. to fix that I will open a separate one.

cc @dulvui

[dulvui]

@leonardehrenfried Great thanks!

[leonardehrenfried]

@slvlirnoff The vector tiles are now available from https://otp.opendatahub.testingmachine.eu/otp/routers/default/vectorTiles/stops,rentalVehicles,rentalVehicles,rentalStations/tilejson.json