Add support for inter-service communications

[oubiwann]

This is for the use case where non-public (no published API ... or docs!) CMR services need to talk to each other. The first thought is that these would go in cmr.client.services.*.

Public services are cmr.client.search, cmr.client.ingest, and cmr.client.access-control. Remaining services, and maybe not all of them would be needed, would include:

• cmr.client.services.bootstrap
• cmr.client.services.common
• cmr.client.services.cubby
• cmr.client.services.index-set
• cmr.client.services.indexer
• cmr.client.services.ingest
• cmr.client.services.metadata-db
• cmr.client.services.moch-echo

The intent is that these would be used for both for writing integration tests as well as features in CMR libs/apps that need to talk to other services.

Furthermore, since these would only be used by the CMR services and libraries themselves, there's no need to make these ClojureScript compatible (e.g., JS in a native app could never make these calls).