Custom Authenticator Fix

Fixes a couple issues preventing custom authenticators from working as expected when using x-amz-customauthorizer-name as the username when making a MQTT connection.

What's Changed

• Update to Samples README to correctly reflect arguments needed by @TwistedTwigleg in #262
• Added ClientToken to ShadowDeltaUpdated by @TwistedTwigleg in #263
• Username query fix by @bretambrose in #264
• Modify AlpnList if using custom authorizer by @TwistedTwigleg in #265

Full Changelog: v1.8.3...v1.8.4