Support declaring non-standard exchange types

[a3kov]

With this change the library will allow declaring non-standard exchange types, such as provided by plugins.

Description

Currently there's no way to define non-standard exchange type. AMQP library allows that via Exchange.declare

Checklist

• [ ] I have added unit tests to cover my changes.
• [ ] I have improved the code quality of this repo. (refactoring, or reduced number of static analyser issues)
• [ ] I have updated the documentation accordingly