Updated examples to use new event id, idf to use mqtt with fixed retained, oversized messages
- Allows placing CI-specific settings into sdkconfig.ci file - Allows substituting environment variables in sdkconfig.ci
added docs and tests for mqtt library, small fixes (removed warnings, option for custom outbox, websocket bug fixed for longer transports). refactored to use common tcp_transport component, support for CMake build system. Closes #2108