Serial: Add support for setting up baudrate

[DhruvaG2000]

inside Serial.begin() we can implement baudrate perhaps using:

• uart_config Struct
• UART controller config structure

[soburi]

@DhruvaG2000
This issue may solve with #64.
Could you confirm it?

[DhruvaG2000]

@soburi thanks for the reminder,
I tested on arduino nano 33 ble sense, with 9600 and 115200 baudrates, setting the baudrate in setup does indeed reflect in reality.
Hence, closing this.