Add LowLevel MQTT Endpoint

[domiko96]

Idea:
Add a lowlevel dircet access MQTT Topic per espled board, where one could send raw bytes for individual leds (not as json). So we can send a full strip state from a Python/Go Application.
We definitely should evaluate the performance and latency along with qos capabilities of mqtt.

To ensure high performance:

• Write directly to Fastled buffer (or PWM Outputs) without copying
• Use raw bytes insead of json -> no parsing and buffer needs