Berry add flash.current_ota

[s-hadinger]

Description:

Berry add flash.current_ota() -> int to know which is the current partition we are running from, typically 0 or 1, or -1 for safeboot. With safeboot layout, it is always 0

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.2.7.6
• The code change is tested and works with Tasmota core ESP32 V.2.0.14
• I accept the CLA.

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