Emit default values when converting message to JSON for display

[will-osborne]

Summary

This change enables visibility of default values in the request and response objects. E.g empty strings and false booleans. what would have show as this before

{
  "foo": "bar"
}

Looks like this after

{
  "foo": "bar",
  "baz": "",
  importantBoolean: false
}

Problem description

Not displaying defalt values is misleading and is against the idioms of GRPC.

Pros/cons of approach implemented

Pros: It's simple and uses existing functionality. Cons: It's non-configurable.

Checklist

• [x] Is this PR a reasonable size?

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