refactor: remove ingest_api/items and ItemPublisher class

[stephenkilbourn]

Issue

closes #568

What?

remove ingest_api/items api route from ingest_api/runtime/src/main.py and ItemPublisher class from ingest_api/runtime/src/collection_publisher.py

Why?

Remove the items endpoint from the ingest API because it is unmaintained and duplicates functionality better covered in the stac-api. Users now have the option to use stac-api transactions for item operations.

[stephenkilbourn]

the test was failing until I updated the Search viewer in stac_api/runtime/src/app.py. from what I can tell, older Starlette versions used positional args (template_name, context, ...), but newer versions expect named parameters (request=..., name=..., context=...). The old positional style failed silently with a 500 during rendering.