AMR: use RESP3 and disable the default config channel by default

[mgravell]

@philon-msft

Specific to AMR endpoints for now (planned more generally for v3)

• prefer RESP3
• don't use the old booksleeve pub/sub channel
• don't run the post-connect maintenance listener hook

Unit test validates behaviour. As a side change: the toy server now supports TLS so we can emulate AMR as closely as possible; we use a self-signed cert for this.

Outstanding:

• pub/sub connections are too eager - need to make lazier, so that even on RESP2 with booksleeve channel disabled:
  1. pub/sub doesn't connect initially
  2. but it does connect when needed