driver: add driver for waveshare RTU relay

[flxzt]

Description

This adds a driver for Waveshare ModbusRTU Relays.
These relays speak modbus so this added driver is dependent on PR #1394 .
In my current setup the relay is used to toggle the power supply of the DUT and to toggle a jumper.
I verified that the added driver works, it has been tested with the cli, the scripting and pytest interface.

Checklist

• Documentation for the feature
• Tests for the feature
• The arguments and description in doc/configuration.rst have been updated
• PR has been tested

[codecov]

Codecov Report

❌ Patch coverage is 60.75949% with 31 lines in your changes missing coverage. Please review.
✅ Project coverage is 46.0%. Comparing base (5818762) to head (1b46a92).
⚠️ Report is 2 commits behind head on master.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
labgrid/driver/modbusrtudriver.py	46.6%	24 Missing ⚠️
labgrid/driver/wavesharerturelaisdriver.py	82.1%	5 Missing ⚠️
labgrid/resource/modbusrtu.py	60.0%	2 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff           @@
##           master   #1441   +/-   ##
======================================
  Coverage    46.0%   46.0%           
======================================
  Files         180     181    +1     
  Lines       14462   14519   +57     
======================================
+ Hits         6654    6686   +32     
- Misses       7808    7833   +25     

Flag	Coverage Δ
3.10	46.0% <60.7%> (+<0.1%)	⬆️
3.11	46.0% <60.7%> (+<0.1%)	⬆️
3.12	46.0% <60.7%> (+<0.1%)	⬆️
3.13	46.0% <60.7%> (+<0.1%)	⬆️
3.14	46.0% <60.7%> (+<0.1%)	⬆️

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