Send proving/consistency checking commands to RabbitMQ

[eugenk]

We want to prove conjectures and check the consistency of OMS in Ontohub. Hets already exposes a REST API to do this with the database. See the initial post of spechub/Hets#1836.

• Extend the GraphQL API by a mutation for proving a conjecture
• Extend the GraphQL API by a mutation for checking the consistency of an OMS
• Form a command for the Hets Agent
• Send the command to the Hets Agent
• Send a response to the HTTP-Client