Feature/nested sub menus in action manager

[Ashwolaa]

Context:
Action manager is very useful and versatile to easily manage QActions and add them to menu/toolbar.
However, it does not necessarily handle well submenus for now making the construction of more complex QMenu quite cumbersome.

In this PR:
We extend Action Manager capabilities by adding the _submenus dict.
This permits to easily store new submenus, attach them to menus and to benefit from the ActionManager methods function.
A little example can be found in examples/action_manager_nested_menu.py

action_manager_menu.mp4

[codecov]

Codecov Report

❌ Patch coverage is 93.15068% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.26%. Comparing base (c66d469) to head (3f976ae).
⚠️ Report is 24 commits behind head on 5.0.x_dev.

Files with missing lines	Patch %	Lines
src/pymodaq_gui/managers/action_manager.py	94.44%	4 Missing ⚠️
src/pymodaq_gui/utils/custom_app.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##           5.0.x_dev     #117      +/-   ##
=============================================
+ Coverage      63.66%   64.26%   +0.60%     
=============================================
  Files             74       73       -1     
  Lines           9077     9132      +55     
=============================================
+ Hits            5779     5869      +90     
+ Misses          3298     3263      -35     

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[seb5g]

why doing things differently on main menu and submenu can we not just consider on only menu argument/dict...

Also by introducing this I guess the setup_menu in custom_app start to be superfluous?

[Ashwolaa]

why doing things differently on main menu and submenu can we not just consider on only menu argument/dict...

There was no reason, I did not want first to touch self._menu but using arg/dict is much better and smoother.
I added a similar mechanism for the toolbars.
The "_default" key would be equivalent to the previous implementation and is the one called when using self._menu / self._toolbar.

Also by introducing this I guess the setup_menu in custom_app start to be superfluous?

I agree, in fact I started to look at it by considering that the ConfigManager could inherit from the ActionManager and build its own QMenu. One can think of standardized QActions for examples, New/Edit/Duplicate/Load/Delete/Open Config folder/ ...).
Then the dashboard would just add to his own QMenuBar, the QMenu created by the ConfigManager.
With this approach, we can more easily connect the available actions with their relevant manager.

[seb5g]

it looks quite nice and neat!