Investigate Blazegraph alternatives that offer horizontal scaling and/or high-availability

**Motivation**
Blazegraph is the single component used by Delta that doesn't support read replicas, failover and sharding. Whenever there's a need for maintenance on the host node or when heavy queries are executed parts of the functionality are no longer available (especially important in multi-tenant scenarios).

**Acceptance criteria**
1. Evaluate other triple stores with support for quads and namespacing (partitioned graphs / databases) that offer sharding, failover and/or read replicas.
2. Provide a comparison table and links to benchmarks (if available)

**Not included**
- setup of potential solution locally