Expand wadge mocking documentation and examples

[brooksmtownsend]

wadge currently allows for developers to write mocking components that implement interfaces for use in testing. It would be great to expand this documentation with examples, at least for common capability provider interfaces like keyvalue and messaging and a custom interface example.

The goal of this issue would be to have some documentation around how to create these mocking components so that users of the wadge framework can create their own mocks.