Add examples to book

[declark1]

We have some in mocktail-tests, but I have received requests to get examples added to the placeholder sections of the book. Creating this issue for tracking.

3.1. Example: HTTP Simple
3.2. Example: HTTP Streaming (ndjson)
3.3. Example: HTTP Streaming (SSE)
3.4. Example: gRPC Unary
3.5. Example: gRPC Client Streaming
3.6. Example: gRPC Server Streaming
3.7. Example: gRPC Bidi Streaming