NI-DCPower: Add examples for electronic loads

[olsl21]

• This contribution adheres to CONTRIBUTING.md.
• I've updated CHANGELOG.md if applicable.
• I've added tests applicable for this pull request

What does this Pull Request accomplish?

• Add nidcpower_constant_resistance_and_constant_power.py and nidcpower_sink_dc_current_into_electronic_load.py
• Regenerate docs/nidcpower/examples.rst
• Update CHANGELOG.md to call out the new examples
• Update the help string for the --option-string parameter to "Option String" based on IVI convention

What testing has been done?

• Unit tests added as part of the example file passed.
• Both tox and tox -c .\generated\nidcpower\tox-system_tests.ini succeeded

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.36%. Comparing base (67b6f7d) to head (86a3d8e).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2103   +/-   ##
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  Coverage   91.35%   91.36%           
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  Files          66       66           
  Lines       16318    16318           
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+ Hits        14908    14909    +1     
+ Misses       1410     1409    -1     

Flag	Coverage Δ
codegenunittests	84.95% <ø> (ø)
nidcpowersystemtests	94.65% <ø> (+0.04%)	⬆️
nidcpowerunittests	89.53% <ø> (ø)
nidigitalsystemtests	92.26% <ø> (ø)
nidigitalunittests	68.44% <ø> (ø)
nidmmsystemtests	92.72% <ø> (ø)
nifakeunittests	87.24% <ø> (ø)
nifgensystemtests	94.86% <ø> (ø)
nimodinstsystemtests	73.85% <ø> (ø)
nimodinstunittests	94.20% <ø> (ø)
niscopesystemtests	92.94% <ø> (ø)
niscopeunittests	43.20% <ø> (ø)
nisesystemtests	91.50% <ø> (ø)
niswitchsystemtests	82.03% <ø> (ø)
nitclksystemtests	94.87% <ø> (ø)
nitclkunittests	98.26% <ø> (ø)

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see 1 file with indirect coverage changes

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[marcoskirsch]

We have a grand total of four nidcpower examples.
This PR increases the number by 50%. Does this seem proportional to you given the relative importance of the products and product features that support this?

[olsl21]

We have a grand total of four nidcpower examples. This PR increases the number by 50%. Does this seem proportional to you given the relative importance of the products and product features that support this?

As discussed previously in our meeting with the stakeholders, Python examples provide value to our customers due to its increased adoption, and hence we should be opportunistic to incrementally add example support for Python for newer products / features, even though it was de-prioritized in the past.

[bkeryan]

We have a grand total of four nidcpower examples. This PR increases the number by 50%. Does this seem proportional to you given the relative importance of the products and product features that support this?

@marcoskirsch I'm surprised there aren't really any examples of basic use cases, similar to NI-DCPower Source DC Voltage.vi or InstrumentStudio's charting mode.

The existing examples seem to demonstrate (somewhat) advanced use cases:

• nidcpower_advanced_sequence.py - advanced sequences are advanced; simple sequences (set_sequence) don't have an example
• nidcpower_lcr_source_ac_voltage.py - only for a specific subset of instruments that support LCR
• nidcpower_measure_record.py - seems like an intermediate use case, so I'm puzzled why this is grpc-device's only nidcpower example: https://github.com/ni/grpc-device/blob/main/examples/nidcpower/measure-record.py . Perhaps this seemed like the simplest nidcpower Python example to use as a starting point.
• nidcpower_source_delay_measure.py - this is pretty close to a basic example, but the emphasis is on setting the source delay and changing the voltage on-the-fly

[ni-jfitzger]

There are several places where you haven't followed Marcos's recommendation to refer to exact symbol names and I believe it hurts the clarity.