Added ability to set a custom routing key per message

[creyke]

As discussed in #51, it is an extremely common requirement to set a routing key of a message based on, for example it's content. The current implementation sets the routing key to the QueueName.

This PR proposes an abstraction in the generic of the IAsyncCollector implementation which enables common meta data related to the message body to be expressed, in this case the RoutingKey.

This is an optional property, and is only used if it is explicitly defined, else normal operation resumes.

[msftclas]

All CLA requirements met.

[pragnagopa]

@creyke - Thanks for the PR! Current design adds support to bind to byte[], which makes it easier for existing users to adopt functions. Tagged @jeffhollan and @fabiocav for further discussion on introducing a wrapper type

[pragnagopa]

@jeffhollan / @fabiocav - Do you recommend introducing a wrapper type 'RabbitMQMessage'

[creyke]

Sorry to chase on this, is it possible to make this adjustment? While I understand this is a API change, I can't imagine many developers could use this library without a meta object, or a way to configure additional details pertaining to and around the message?

[fabiocav]

@creyke apologies for the delayed response. We're reviewing the open PRs that have gone stale (not your fault) in the repo.

Is this still relevant? Do you know if there's a specific reason why the SDK doesn't expose that? (sorry, haven't looked at the details, just assuming it would be needed there as well, unless it's provided as part of a method call).

[creyke]

Hi @fabiocav, thanks for picking this up.

I believe this has not been exposed yet due to the most basic of use cases not requiring it.

Anyone using topic exchanges will require control over the routing key.

If this can come in I'm confident many more customers can move over to this library, and it will not overly complicate the use cases for users which do not need to define it.