Changed internal macro APP_SLEEP to TASMOTA_SLEEP to specify default sleep in ms

[s-hadinger]

Description:

Due to the way APP_SLEEP worked, it was anyways defaulted to 50ms.

It is renamed to TASMOTA_SLEEP to avoid collision, and allows now the precise value to be changed as the default value of pre-compiled firmwares.

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.3.0.0
• I accept the CLA.

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