Add Zigbee router firmware for Sonoff ZBBridgePro

[s-hadinger]

Description:

Add router only firmware for Sonoff ZBBridgePro. This is just the Koenkk firmware with BSL gpio changed from DIO_15 to DIO_8.

Checklist:

• The pull request is done against the latest development branch
• Only relevant files were touched
• Only one feature/fix was added per PR and the code change compiles without warnings
• The code change is tested and works with Tasmota core ESP8266 V.2.7.4.9
• The code change is tested and works with Tasmota core ESP32 V.2.0.5
• I accept the CLA.

NOTE: The code change must pass CI tests. Your PR cannot be merged unless tests pass