New features oriented to improve index procedure efficiency

During indexing, all we need are the node properties from Neo4j directly AND a few on_read_trigger generated ones. But the current GET /entitites/<id> returns ALL trigger generated properties, totally inefficient and unnecessary. And the index procedure has to remove the ones that are not specified in the mapping json with lots of for loops, such repetitive work is a total waste of time and further reduces the efficiency.

To address the above issues in the entity-api,

Introduce a new trigger type: on_index_trigger, which has the same trigger method as regular on_read_trigger.
Add a specialized schema_manager method get_complete_document_result() which is very similar to get_complete_entity_result() (for now do NOT modify this method), but uses on_index_trigger instead.
For caching, use a different prefix on those index data, cache_key = f'{_memcached_prefix}_complete_index_{entity_uuid}'
Introduce a new flag in schema yaml indexed: false (default is true) for indexing purposes. This allows us to remove the use of json mapping in search-api. When exposed: false there's no need to check this indexed: false since it's a field won't be exposed by entity-api. When there's only indexed: false it means this field still gets returned to the regular GET call, but we won't index this field.
Add a specialized schema_manager method normalize_document_result_for_response() based on the current normalize_entity_result_for_response() and integrate with the indexed flag.

Afterwards, create a specialized endpoint (based on the current GET /entities/<id> but with no property filtering needed): GET /documents/<id> which returns a subset of the regular entity json to be used for index, without including the following generated fields (not used by index process):

Donor: None, since no on_read_trigger
Sample: direct_ancestor
Dataset/Publication (including revisions): collections, upload, direct_ancestors, local_directory_rel_path
Publication-specific: ~~associated_collection~~ (still need this field to be indexed)

AFTER the new features get tested, switch to use this new endpoint in search-api: https://github.com/hubmapconsortium/search-api/issues/756

sennetconsortium / entity-api

New features oriented to improve index procedure efficiency #396