Update BME280 driver and MQTT TLS tutorial

[floitsch]

Summary

• migrate the BME280 tutorial and mirrored examples to the bmx280 driver
• use Mosquitto TLS port 8886 so common trusted roots validate the broker certificate
• update the documentation snippet-checker dependencies

Testing

• toit analyze -Werror for the affected tutorial examples and snippet checker
• ESP32 hardware rig bmx280 test on Board 2
• bounded live MQTT publish/subscribe test against test.mosquitto.org:8886
• Gatsby production build
• git diff --check