Add relationship only ingestion to the model to produce many to many relationships on a single run

[heryxpc]

Model relationships that can be loaded without a node schema

Currently, the load function needs a CartographyNodeSchema to ingest the data from a dictionary to the Cypher queries inserting the data.

It would enable different possibilities to have a load function that can create the Cypher queries using relationship definitions only.

This would enable modules that can perform analysis of data and enrich existing nodes. A few examples are:

• Connect GithubUser to OktaUser to LastpassUser
• Identify duplicate AWS:DNSRecord and GCPDNSZone

If done generic enough, this could also improve ingestion of 1 to many relationships to improve performance on ingestion:

• Multiple (GitHubUser)-[: OWNER| OUTSIDE_COLLAB_*| DIRECT_COLLAB_*]-(GitHubRepository) relations

[heryxpc]

@jychp feel free to add or update with the references you already have for relationship ingestion.

[jychp]

will try to extract and format info from this PR discussion: #1465