Feature/issue 307 async write api

[iverasp]

Summary

Adds a async write api that ingests stops in netex format. DTO accepts a list of stops, but only a single stop is supported for now.
Extracts verification logic when updating a stop on the graphql endpoint and reuses it for this api.
Uses a facade so it will be easier to add other entrypoints such as pubsub in the future.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update (changes to documentation only)
• Other (please describe)

Issue

#307

Unit tests

Write a few words on how the new code is tested.

• Were unit tests added/updated?
• Was any manual verification done?
• Any observations on changes to performance?
• Was the code designed so it is unit testable?
• Were any tests applied to the smallest appropriate unit?
• Do all tests
  pass the continuous integration service?

Documentation

The generated openapi specification includes examples of requests.