Implement logging widget (mostly for devs)

[edan-bainglass]

This PR adds a flag, which if True, adds an Output widget at the bottom of the app, accompanied by a reset button. The widget can then be passed down to any part of the app that needs to be tested.
The PR hardcodes one use-case - monitoring. The ProcessMonitor was recently changed (aiidalab/aiidalab-widgets-base#669) to accept an output widget and use it to log exceptions in monitored callbacks. This PR passes the output widget (if included) down to the ProcessMonitor instance, exposing its exceptions. This is useful for debugging issues in the results step.

[codecov]

Codecov Report

Attention: Patch coverage is 27.27273% with 8 lines in your changes missing coverage. Please review.

Project coverage is 71.92%. Comparing base (e3e7816) to head (805ddab).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/aiidalab_qe/app/main.py	0.00%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1133      +/-   ##
==========================================
- Coverage   71.99%   71.92%   -0.07%     
==========================================
  Files         105      105              
  Lines        6877     6886       +9     
==========================================
+ Hits         4951     4953       +2     
- Misses       1926     1933       +7     

Flag	Coverage Δ
python-3.11	71.92% <27.27%> (-0.07%)	⬇️
python-3.9	71.93% <27.27%> (-0.07%)	⬇️

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[superstar54]

Very useful! thanks!