[FR] Discard DB IRIS_TASKS and use main POSTGRES_DB or at least replace the hard coded db name with a configurable one

[StaSys846]

Please ensure your feature request is not already on the roadmap or associated with an issue. This can be checked here.

Is your feature request related to a problem? Please describe.
Currently IRIS uses two databases: A DB with configurable name via POSTGRES_DB env var and a second hard coded DB with the name "IRIS_TASKS" (defined in iris post_init source code). When deploying multiple IRIS instances (e.g dev/prod) on a single postgres cluster (e.g. AWS RDS) both IRIS instances interfere and want to use the same hard coded DB (each instance needs its own IRIS_TASKS db).

Describe the solution you'd like
Either use additional tables (used in the IRIS_TASKS db) in the already existing main DB with the name defined by POSTGRES_DB env var (preferred) or use a configurable name for the IRIS_TASKS db (e.g. by an additional env var).

Additional context
Currently unclear why a second DB is needed at all. And when inherently needed, make the DB name customizable.