Allow setting session items when calling InjectApplicationMessage

[tboothman]

Describe the feature request

Allow the user to specify the session items in the virtual session for the server when injecting application messages.

Background:
We inject MQTT messages using InjectApplicationMessage but since 4.0 the InterceptingPublishAsync hook is called for injected messages. We check the session for metadata about the client to see if they're allowed to publish, which is now just an empty dictionary so it gets rejected.

Which project is your feature request related to?

• Server

Describe the solution you'd like

The method InjectApplicationMessage to take an argument for session items

Describe alternatives you've considered

Set the session items on the server and just use that for every InjectApplicationMessage. There's a property called _sessionItems with an empty dictionary that's currently used as the session. Could add a method to change that property..