Provide access to the message router options via the message pump options for custom message router implementations

[stijnmoreels]

Is your feature request related to a problem? Please describe.
When implementing a custom IAzureServiceBusMessageRouter, we can't use the same configureMessagePump function (message router options are part of the message pump options in this case), because the message router options are internal in the message pump options.

Describe the solution you'd like
We should consider making this MessageRouterOptions property either public or something in this line, so we can re-use the configureMessagePump function and therefore configure the message router the same way.

Additional context

arcus.messaging/src/Arcus.Messaging.Pumps.ServiceBus/Configuration/AzureServiceBusMessagePumpOptions.cs

Line 112 in 7b46969

internal AzureServiceBusMessageRouterOptions MessageRouterOptions { get; } = new AzureServiceBusMessageRouterOptions();