Use Tiamat directly from Hasura as a read-only database

[culka]

The database of Tiamat can be used direclty by Hasura, to easily enable more complex data selection. This will it possible to implement the planned search feature in full capacity.

Insert and update mutations should still be done through Tiamat, to preserve the version structure and netex export capabilities.

• Create a read-only role for Hasura in the database
• Add a direct connection to the database
• Use a different name for the database from the previous Tiamat remote schema

Relates to the search entity. This blocks #1305 ticket.