feat: Add write operation handlers for coils and registers

[zhongys-c8y]

Added set_coil.py and set_register.py under tedge_modbus for writing values to modbus. One for register, one for coil. In the reader.py, added on_message function to subscribe to the tedge local MQTT topics of child devices' operations. The operation payload was based on the internal docs 'cloud fieldbus specification'. The c8y operation will be first mapper from c8y/devicecontrol/notifications topic to tedge local topics by using tedge custom operation template.

It was tested with the simulator in this project. It can successfully change the register and coil value.

[reubenmiller]

Approved. Thanks for the nice contribution. We can extend the documentation for this feature in a new PR.

FYI: We created a new PR from #37 to clean up the history and reworked the fork's main branch.

[github-actions]

Robot Results

✅ Passed	❌ Failed	⏭️ Skipped	Total	Pass %	⏱️ Duration
22	0	0	22	100	44.264329s

Passed Tests

Name	⏱️ Duration	Suite
Device should support the operation c8y_ModbusConfiguration	0.170 s	Device
Set values via c8y_ModbusConfiguration Operation	2.456 s	Operation
Poll rate and transmit rate should be updated for the Device	0.270 s	Operation
Poll rate and transmit rate should be updated on the Device	2.495 s	Operation
Device should support the operation c8y_ModbusDevice	0.146 s	Device
Device should support the operation c8y_SerialConfiguration	0.147 s	Device
Set values via c8y_SerialConfiguration Operation	2.467 s	Operation
Serial configuration should be updated for the Device	0.269 s	Operation
Serial configuration should be updated on the Device	2.451 s	Operation
Device should have installed software tedge-modbus-plugin	0.159 s	Debian
Service should be active	2.458 s	Debian
ReInstall Modbus Plugin	23.698 s	Debian
Device should have the fragment c8y_ModbusConfiguration	0.294 s	Device
ChildDevice TestCase1 should be created	0.281 s	Device
ChildDevice TestCase1 should have the fragment c8y_ModbusDevice	0.706 s	Device
Service tedge-modbus-plugin should be enabled	0.146 s	Device
Device should set supported operations for writing to registers and coils	0.142 s	Operations
Device should write to a registers	2.467 s	Operations
Device should write to a coil	2.463 s	Operations
ChildDevice TestCase1 should have a Test.Int16 Measurement	0.291 s	Telemetry
ChildDevice TestCase1 should have a Test.Float32 Measurement	0.288 s	Telemetry
ChildDevice TestCase1 should have Alarms of type TestAlarm on Coil Value 1	0.001 s	Telemetry