Collection update endpoint supports merge

[smohiudd]

Why

Aggregated information such collection summaries of item dates and spatiotemporal extent updates based on contained items inserted by our ingestion pipelines could be lost if replacing a collection record.

Description

A "merge" operation should be supported in the ingest API (and STAC Transactions extension?) that maintains existing aggregated metadata when replacing or updating a collection record. This logic could merge the existing summaries object with a new STAC collection.

Acceptance Criteria

• Ingestion API /collections POST endpoint includes logic to merge existing aggregating metadata if it exists

[anayeaye]

related: stac-utils/stac-fastapi#744