Wire JSON ingestion schema extension modules

[jwils]

Why

Introduce the JSON ingestion schema-definition extension modules after the indexing extension points exist, but before making JSON ingestion the default implementation.

What

• Add ElasticGraph::JSONIngestion::SchemaDefinition::APIExtension and supporting factory/results/artifact/state/schema-element extension modules
• Wire JSON ingestion through the factory so core indexing field references and field types are extended in place
• Keep the existing core JSON Schema behavior active in this intermediate layer
• Add doctest support for JSON ingestion schema-definition examples without making the extension the default yet

Risk Assessment

Medium - this adds new extension code, but the default behavior remains the existing core JSON Schema implementation in this PR.

References

• Stacked on Add JSON ingestion indexing extensions #1204.
• bundle exec rspec elasticgraph-schema_definition/spec/unit/elastic_graph/schema_definition/json_schema_spec.rb elasticgraph-schema_definition/spec/unit/elastic_graph/schema_definition/json_schema_field_metadata_spec.rb elasticgraph-schema_definition/spec/unit/elastic_graph/schema_definition/indexing/json_schema_with_metadata_spec.rb elasticgraph-schema_definition/spec/unit/elastic_graph/schema_definition/factory_spec.rb passed.
• script/type_check passed.
• script/lint passed.

Stack

Current PR is marked with ->.

• #1199 Add JSON ingestion gem shell
• #1200 Add schema definition extension plumbing
• #1201 Move JSON schema helpers to json ingestion gem
• #1203 Namespace JSON schema helpers under JSON ingestion
• #1204 Add JSON ingestion indexing extensions
• -> #1215 Wire JSON ingestion schema extension modules
• #1205 Use JSON ingestion as schema definition extension
• #1202 Document JSON ingestion schema APIs
• #1224 Migrate JSON ingestion specs into gem
• #1220 Add configurable indexing event decoder

[myronmarston]

I haven't finished reviewing but wanted to submit my feedback so far.

[myronmarston]

Still not done reviewing but here's my next round of feedback.

[myronmarston]

Next set of feedback (still not done reviewing!).

[myronmarston]

Made it through the end of my review this time! Almost ready.