Add accordion component

[clarasb]

This PR:

• adds a Accodion component to the mui plugin.
• adds a demo panel to showcase the component.

Notes:

• AccordionActions is not supported yet.
• The current implementation focuses on summary and details of Accordion only.

Mentioned in Widget Wishlist (#41).
Closes #134.

---

Demo Panel I:

[b-yogesh]

Thanks, looks good. Please have a look at my comments.

[b-yogesh]

Does this mean we can have multiple children for this component? How does that look like?

[clarasb]

Yes, the Accordion component accepts multiple children, which are rendered in the order they are provided. Additional styling can be applied via the style prop.

[codecov]

Codecov Report

❌ Patch coverage is 95.83333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 92.27%. Comparing base (794871e) to head (975bfc2).
⚠️ Report is 14 commits behind head on main.

Files with missing lines	Patch %	Lines
...lets.js/packages/lib/src/plugins/mui/Accordion.tsx	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #140      +/-   ##
==========================================
+ Coverage   92.22%   92.27%   +0.05%     
==========================================
  Files          87       89       +2     
  Lines        1504     1528      +24     
  Branches      231      236       +5     
==========================================
+ Hits         1387     1410      +23     
- Misses         98       99       +1     
  Partials       19       19              

Flag	Coverage Δ
backend	100.00% <100.00%> (ø)
frontend	83.98% <88.88%> (+0.06%)	⬆️

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[b-yogesh]

Thank you for applying the change requests. Can you just attach the screenshot of the updated demo with multiple children? Feel free to merge after that.