Configurable server keep alive intervals

[rompetroll]

Depending on how and where datahub is deployed, it can be necessary to modify the default server keep-alive settings.
An example use case is the interaction with load balancers during long running requests.

Datahub could provide options similar to these https://www.postgresql.org/docs/current/runtime-config-connection.html#GUC-TCP-KEEPALIVES-IDLE.

Here an idea for how to modify tcp listener settings.
labstack/echo#1942