Fixes Issue #1699 | CommandProcessor.Call(..) works again

[DevJonny]

CommandProcessor.Call(..) wasn't working because the individual gateways didn't support the generic Subscription only specific for that gateway. The following changes have been made:

• ServiceCollectionExtensions.UseExternalBus(..) now takes in an optional IEnumerable<Subscription> for each reply queue type
• On invocation of .Call(..) the appropriate Subscription is grabbed, and the RoutingKey and ChannelName are set to a new GUID
• Fixes ServiceCollectionsExtensions to supply an Outbox when using RPC
• Updates the RMQRequestReply sample to use the new changes

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[iancooper]

Thanks. This is a great fix.