Add support for modifying execution settings for Julia and Python Tool Specifications

[ptsavol]

Re spine-tools/Spine-Toolbox#2446

Checklist before merging

• [x] Documentation (also in Toolbox repo) is up-to-date
• [x] Release notes in Toolbox repo have been updated
• [ ] Unit tests have been added/updated accordingly
• [x] Code has been formatted by black
• [x] Unit tests pass

[codecov-commenter]

Codecov Report

Attention: 91 lines in your changes are missing coverage. Please review.

Comparison is base (d0aa796) 60.27% compared to head (319eaa3) 60.12%.

Files	Patch %	Lines
...e_items/tool/widgets/tool_spec_optional_widgets.py	41.02%	43 Missing and 3 partials :warning:
...s/tool/widgets/tool_specification_editor_window.py	22.50%	31 Missing :warning:
spine_items/tool/tool_specifications.py	31.57%	13 Missing :warning:
spine_items/tool/tool.py	0.00%	1 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## 0.8-dev #179 +/- ## =========================================== - Coverage 60.27% 60.12% -0.15% =========================================== Files 194 194 Lines 17692 17853 +161 Branches 2888 2914 +26 =========================================== + Hits 10663 10734 +71 - Misses 6462 6549 +87 - Partials 567 570 +3 ```

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