examples: add client example for tonic-reflection

[grottohub]

This adds an example usage of the ServerReflectionClient using a ListServices request.

Fixes: #1600

Motivation

Took awhile to figure out how to set up the reflection client, so thought I would provide an example.

Solution

This example includes everything needed to communicate with a server providing reflection:

• setting up the client with an Endpoint (since the codegen doesn't provide the connect method most clients have as transport is an optional feature for tonic-reflection)
• configuring a ServerReflectionRequest using one of the provided MessageRequest options
• putting the request into a stream since reflection is a bidi-streaming procedure
• parsing the response received from the server