Add MemoryHub as an AMB memory provider

[rdwj]

MemoryHub is a Kubernetes-native agent memory component for OpenShift AI. Stores verbatim conversations and retrieves via hybrid vector + keyword search with cross-encoder reranking and reciprocal-rank fusion. PostgreSQL + pgvector backend, Apache 2.0 licensed.

I'd like to contribute a provider adapter and PersonaMem 32k results (83.7%). PR incoming.

• Repository: https://github.com/redhat-ai-americas/memory-hub
• Kind: cloud (self-hostable on OpenShift/Kubernetes, accessed via MCP SDK)