Added docs for write operations

[zhongys-c8y]

Added some docs for the write operation handle of new name-based format.

[github-actions]

Robot Results

✅ Passed	❌ Failed	⏭️ Skipped	Total	Pass %	⏱️ Duration
24	0	0	24	100	45.276853999s

Passed Tests

Name	⏱️ Duration	Suite
Device should support the operation c8y_ModbusConfiguration	0.103 s	Device
Set values via c8y_ModbusConfiguration Operation	2.445 s	Operation
Poll rate and transmit rate should be updated for the Device	0.229 s	Operation
Poll rate and transmit rate should be updated on the Device	2.412 s	Operation
Device should support the operation c8y_ModbusDevice	0.103 s	Device
Device should support the operation c8y_SerialConfiguration	0.103 s	Device
Set values via c8y_SerialConfiguration Operation	2.406 s	Operation
Serial configuration should be updated for the Device	0.191 s	Operation
Serial configuration should be updated on the Device	2.412 s	Operation
Device should have installed software tedge-modbus-plugin	0.156 s	Debian
Service should be active	2.413 s	Debian
ReInstall Modbus Plugin	20.983 s	Debian
Device should have the fragment c8y_ModbusConfiguration	0.208 s	Device
ChildDevice TestCase1 should be created	0.273 s	Device
ChildDevice TestCase1 should have the fragment c8y_ModbusDevice	0.491 s	Device
Service tedge-modbus-plugin should be enabled	0.171 s	Device
Device should set supported operations for writing to registers and coils	0.098 s	Operations
Device should write to a register using explicit address format	2.432 s	Operations
Device should write to a register referenced by name	2.415 s	Operations
Device should write float value to register referenced by name	2.405 s	Operations
Device should write to a coil	2.423 s	Operations
ChildDevice TestCase1 should have a Test.Int16 Measurement	0.201 s	Telemetry
ChildDevice TestCase1 should have a Test.Float32 Measurement	0.201 s	Telemetry
ChildDevice TestCase1 should have Alarms of type TestAlarm on Coil Value 1	0.001 s	Telemetry