Doc: Support restart of the broker when it looses connection to the database

Currently, when the AMQ broker looses the connection to the database, it immediately shuts down.

This is a request raised to support a restart feature such that the broker should try to restart itself and then connect to the secondary database.

In AMQ6, there was a parameter "restartAllowed".

This request is also raised in the context of

if the broker is configured with JDBC persistence using Oracle in HA mode (JDBC Persistence - Oracle Data guard in Grid deployment) .

The expectation is that When Primary Database goes down, broker should switch over to Secondary database.

However the broker instance gets stopped the moment primary DB goes down.

The switch from primary to secondary takes rough 45 seconds and the restart of the broker could connect to the secondary database