Show images for FIELD std_dev in the plotter

[frode-aarstad]

Issue Resolves #7494

Approach Short description of the approach

(Screenshot of new behavior in GUI if applicable)

• [ ] PR title captures the intent of the changes, and is fitting for release notes.
• [ ] Added appropriate release note label
• [ ] Commit history is consistent and clean, in line with the contribution guidelines.
• [ ] Make sure tests pass locally (after every commit!)

When applicable

• [ ] When there are user facing changes: Updated documentation
• [ ] New behavior or changes to existing untested code: Ensured that unit tests are added (See Ground Rules).
• [ ] Large PR: Prepare changes in small commits for more convenient review
• [ ] Bug fix: Add regression test for the bug
• [ ] Bug fix: Create Backport PR to latest release

[frode-aarstad]

For the test_field_param_update test in test_field_parameter.py the following is generated:

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 57.63889% with 61 lines in your changes are missing coverage. Please review.

Project coverage is 85.39%. Comparing base (ed89624) to head (84747a5). Report is 1 commits behind head on main.

Files	Patch %	Lines
src/ert/gui/plottery/plots/std_dev.py	38.70%	19 Missing :warning:
src/ert/gui/tools/plot/plot_window.py	54.28%	16 Missing :warning:
src/ert/dark_storage/endpoints/records.py	28.57%	10 Missing :warning:
src/ert/gui/tools/plot/plot_api.py	10.00%	9 Missing :warning:
src/ert/gui/tools/plot/plot_widget.py	86.66%	4 Missing :warning:
src/ert/dark_storage/common.py	80.00%	2 Missing :warning:
src/ert/gui/plottery/plot_context.py	83.33%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7502      +/-   ##
==========================================
- Coverage   85.56%   85.39%   -0.18%     
==========================================
  Files         382      383       +1     
  Lines       23390    23507     +117     
  Branches      876      876              
==========================================
+ Hits        20014    20074      +60     
- Misses       3262     3319      +57     
  Partials      114      114              

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[dafeda]

[frode-aarstad]