Optimization: `SqlImplementation.relationships_metadata()`

## Overview
@cmungall recently added _ability to retrieve axiom annotations on relationships_ (#656), but there is a significant performance bottleneck. I noticed this during my [`mondo-ingest` synchronization pipeline work](https://github.com/monarch-initiative/mondo-ingest/pull/363#discussion_r1336501888). This operation was taking 104 minutes to complete.

## Possible solutions
- #659

Start by locating SqlImplementation.relationships_metadata() and read the performance context from mondo-ingest synchronization work. Review the possible solution in issue #659 and compare its approach with the current operation. Done means the relationship metadata retrieval no longer has the reported performance bottleneck, with validation based on the synchronization workflow.

Written by the indexing model from the issue text.