driver/power: add support for Siglent SPD3000X series power supplies

[esben]

Description

Add support for using Siglent SPD3000X series power supplies, such as SPD3303X and SPD3303X-E with NetworkPowerDriver.

Checklist

• Documentation for the feature
• Tests for the feature
• CHANGES.rst has been updated
• PR has been tested

[codecov]

Codecov Report

Merging #717 (9350e58) into master (86c112c) will decrease coverage by 0.0%.
The diff coverage is 20.0%.

@@           Coverage Diff            @@
##           master    #717     +/-   ##
========================================
- Coverage    58.7%   58.7%   -0.1%     
========================================
  Files         130     131      +1     
  Lines        9330    9345     +15     
========================================
+ Hits         5484    5486      +2     
- Misses       3846    3859     +13     

Impacted Files	Coverage Δ
labgrid/driver/power/siglent.py	20.0% <20.0%> (ø)
labgrid/util/agentwrapper.py	96.5% <0.0%> (-1.2%)	⬇️

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[jluebbe]

Also, your Signed-off-by is missing.

[jluebbe]

The CI issue is unrelated and was fixed with #721.