Implement discharge capacity as an optional x-axis in QuickPlot

[medha-14]

Description

Fixes #1751

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #) - note reverse order of PR #s. If necessary, also add to the list of breaking changes.

• New feature (non-breaking change which adds functionality)
• Optimization (back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)

Key checklist:

• No style issues: $ pre-commit run (or $ nox -s pre-commit) (see CONTRIBUTING.md for how to set this up to run automatically when committing locally, in just two lines of code)
• All tests pass: $ python -m pytest (or $ nox -s tests)
• The documentation builds: $ python -m pytest --doctest-plus src (or $ nox -s doctests)

You can run integration tests, unit tests, and doctests together at once, using $ nox -s quick.

Further checks:

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[medha-14]

I have implemented the necessary changes for handling 0D variables. Once this is confirmed to be working correctly, I plan to work on handling 1D and 2D variables. Additionally, I have made changes in the dynamic plot, though I am unsure if they were necessary, so I would appreciate it if you could review them as well. Could you please suggest the next steps for moving forward?

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 17 lines in your changes missing coverage. Please review.

Project coverage is 98.62%. Comparing base (ef8571c) to head (ffe69f6).

Files with missing lines	Patch %	Lines
src/pybamm/plotting/quick_plot.py	50.00%	17 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #4775      +/-   ##
===========================================
- Coverage    98.69%   98.62%   -0.08%     
===========================================
  Files          303      303              
  Lines        23226    23252      +26     
===========================================
+ Hits         22923    22932       +9     
- Misses         303      320      +17     

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