Berry zigbee.find()

[s-hadinger]

Description:

Berry Zigbee, add zigbee.find(shortaddr:int | friendlyname:str) -> instance of zb_device as an alternative to zigbee[shortaddr:int | friendlyname:str], but find returns nil when the device does not exist, instead of an exception.

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.2.7.7
• The code change is tested and works with Tasmota core ESP32 V.3.0.2
• I accept the CLA.

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