Remove redundant metadata (#685)

The metadata field (list of triples) in the pipeline Metadata class
was redundant. Document metadata triples already flow directly from
librarian to triple-store via emit_document_provenance() - they don't
need to pass through the extraction pipeline.

Additionally, chunker and PDF decoder were overwriting metadata to []
anyway, so any metadata passed through the pipeline was being
discarded.

Changes:
- Remove metadata field from Metadata dataclass
  (schema/core/metadata.py)
- Update all Metadata instantiations to remove metadata=[]
  parameter
- Remove metadata handling from translators (document_loading,
  knowledge)
- Remove metadata consumption from extractors (ontology, agent)
- Update gateway serializers and import handlers
- Update all unit, integration, and contract tests

trustgraph-flow/trustgraph/librarian/service.py

@@ -334,7 +334,6 @@ class Processor(AsyncProcessor):
             triples_msg = Triples(
                 metadata=Metadata(
                     id=doc_uri,
-                    metadata=[],
                     user=processing.user,
                     collection=processing.collection,
                 ),
@@ -381,7 +380,6 @@ class Processor(AsyncProcessor):
                 doc = TextDocument(
                     metadata = Metadata(
                         id = document.id,
-                        metadata = document.metadata,
                         user = processing.user,
                         collection = processing.collection
                     ),
@@ -392,7 +390,6 @@ class Processor(AsyncProcessor):
                 doc = TextDocument(
                     metadata = Metadata(
                         id = document.id,
-                        metadata = document.metadata,
                         user = processing.user,
                         collection = processing.collection
                     ),
@@ -408,7 +405,6 @@ class Processor(AsyncProcessor):
                 doc = Document(
                     metadata = Metadata(
                         id = document.id,
-                        metadata = document.metadata,
                         user = processing.user,
                         collection = processing.collection
                     ),
@@ -419,7 +415,6 @@ class Processor(AsyncProcessor):
                 doc = Document(
                     metadata = Metadata(
                         id = document.id,
-                        metadata = document.metadata,
                         user = processing.user,
                         collection = processing.collection
                     ),