[FR] Start PoC of GraphQL

[whikernel]

Create a new endpoint leveraging GraphQL to test the feasibility

[c8y3]

Some things we have to take into consideration:

• the choice of COTS must be consistent with the existing application
• check than GraphQL can be integrated with the current implementation of authentication
• GraphQL does not allow file download => an alternative must be find for the datastore files
• http default cache is not useful with GraphQL
• documentation
• end-to-end tests