Select component: add prop multiple

[clarasb]

This PR closes #101.

This PR:

• adds the prop multiple to the Select Component

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.39%. Comparing base (fe89934) to head (f60370e).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #102      +/-   ##
==========================================
+ Coverage   89.36%   89.39%   +0.03%     
==========================================
  Files          84       84              
  Lines        1438     1443       +5     
  Branches      213      217       +4     
==========================================
+ Hits         1285     1290       +5     
  Misses        124      124              
  Partials       29       29              

Flag	Coverage Δ
backend	100.00% <100.00%> (ø)
frontend	77.06% <100.00%> (+0.10%)	⬆️

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[forman]

Cool, thanks!

• Please add an entry to CHANGES.md.
• Always form Python code using "black" (or "ruff") and for TS use "prettier"

[forman]

• do not format entire CHANGES.md files only because you added a new item
• avoid updating package-lock.json when package.json hasn't changed

EDIT

In addition:

• the formatting of TypeScript files uses a wrong style, use prettier
• Select.tsx coverage dropped by ~5%, please add a test case that covers the multiple property

[b-yogesh]

Overall it looks good. Please have a look at my comments and change requests. Thanks :)

[b-yogesh]

I would prefer if we limit the number of demo's here, as there is already some backlog with a few more demos. It would be good, if we can add your demo to Panel C as it already has a Select element, and you can now show that we can use multiple elements by updating the text accordingly (which is also very similar to your demo).

[forman]

I'd prefer, if no longer continue that way. In another pull request we should rearrange the demo app entirely.