Fix dc2d: Pseudosection and add warning in examples for the observation file format

[thast]

• Pseudosection failed to plot for Wenner array
• In the example, the observations file to build the survey is assumed to be sorted by sources, but it was not mention anywhere. I added a warning regarding that.

Thank you ericjohnson on discourse for pointing us those issues.

TODO: rename from_ambn_locations_to_survey to from_abmn_locations_to_survey

[codecov]

Codecov Report

Merging #969 (285b7e4) into main (055ca54) will increase coverage by 0.00%.
The diff coverage is 55.55%.

@@           Coverage Diff           @@
##             main     #969   +/-   ##
=======================================
  Coverage   78.79%   78.79%           
=======================================
  Files         173      173           
  Lines       20720    20723    +3     
=======================================
+ Hits        16326    16329    +3     
  Misses       4394     4394           

Impacted Files	Coverage Δ
...mPEG/electromagnetics/static/utils/static_utils.py	71.74% <0.00%> (ø)
SimPEG/electromagnetics/static/resistivity/IODC.py	48.38% <71.42%> (+0.33%)	⬆️

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