Open the default Python or Julia in the Basic Console

[ptsavol]

This PR adds two new buttons to the Main Windows' Consoles menu. The other one opens the default Python in a 'detached' Basic Console, and the other one opens the default Julia in a 'detached' Basic Console. These are intended, for example, for a quick check if the selected environments are ready before you execute a full workflow. The default Python and Julia are defined in the app settings (File->Settings->Tools).

Fixes no issue.

Checklist before merging

• Documentation is up-to-date
• Release notes have been updated
• Unit tests have been added/updated accordingly
• Code has been formatted by black & isort
• Unit tests pass

[codecov]

Codecov Report

Attention: Patch coverage is 63.72549% with 74 lines in your changes missing coverage. Please review.

Project coverage is 67.35%. Comparing base (fcaa2a0) to head (2102cb1).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
spinetoolbox/widgets/persistent_console_widget.py	57.89%	50 Missing and 6 partials ⚠️
spinetoolbox/ui_main.py	68.00%	12 Missing and 4 partials ⚠️
spinetoolbox/helpers.py	66.66%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3033      +/-   ##
==========================================
+ Coverage   67.12%   67.35%   +0.22%     
==========================================
  Files         193      193              
  Lines       37082    37233     +151     
  Branches     4447     4472      +25     
==========================================
+ Hits        24893    25079     +186     
+ Misses      10931    10876      -55     
- Partials     1258     1278      +20     

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