Flash firmware without run build

[Jason2866]

Description:

This change makes mass deployment flashing possible with VSC and Platformio IDE.

The existing firmware in build_output is flashed without any other Platformio task is done.
Select the env you want to flash and click Upload in Tasmota VSC bottom menu bar.

This can be repeated to flash devices (with same firmware) as often it is needed.

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.2.0.7
• I accept the CLA.

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