Add database to documentation

Before implementing the InciManager and InciDashboard we thought that a shared database would not be needed (we thought Kafka was enough). While it is possible to avoid using a shared database (using materialized views and Kafka streams instead), it made it easier for us to develop the modules.

So now we must add information about the shared database in the respective sections of the documentation.

Locate the documentation sections for InciManager and InciDashboard and review how Kafka and the current architecture are described. Add the shared database information to those respective sections, then verify that both sections consistently explain the database choice.

Written by the indexing model from the issue text.