Improve marketplace vendors behavior

[xavierfacq]

Description of change

This PR is a proposal to improve the Vendors code in the Marketplace page (following the #2131)

• loading of the vendor list & avoid double load of the list at startup
• normalize variables in DownloadDropdowns/index.tsx
• improve the vendor JSON to add the 'identifier' of the vendor
• DownloadDropdowns is now using a list of selected vendor identifiers and NOT a list of ref to HTML objects ( 😱 )
• getAllPkgsForVersion() method receives now a list of vendor identifiers and NOT a list ref to HTML objects ( 😱 )

Generally speaking: make the code easier to understand and maintain in the future

Checklist

• npm test passes

[netlify]

✅ Deploy Preview for eclipsefdn-adoptium ready!

Name	Link
🔨 Latest commit	1f0f0a7
🔍 Latest deploy log	https://app.netlify.com/sites/eclipsefdn-adoptium/deploys/64eb8a86d39f430008b4123d
😎 Deploy Preview	https://deploy-preview-2168--eclipsefdn-adoptium.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[codecov]

Codecov Report

Merging #2168 (1f0f0a7) into main (3cad9b7) will decrease coverage by 0.01%.
Report is 12 commits behind head on main.
The diff coverage is 97.61%.

@@            Coverage Diff             @@
##             main    #2168      +/-   ##
==========================================
- Coverage   99.17%   99.17%   -0.01%     
==========================================
  Files          85       86       +1     
  Lines        6306     6294      -12     
  Branches      531      536       +5     
==========================================
- Hits         6254     6242      -12     
  Misses         52       52              

Files Changed	Coverage Δ
src/components/VendorSelector/index.tsx	98.03% <96.15%> (-1.97%)	⬇️
src/components/DownloadDropdowns/index.tsx	93.91% <100.00%> (+0.43%)	⬆️
src/hooks/fetchMarketplace.tsx	100.00% <100.00%> (ø)
src/util/vendors.tsx	100.00% <100.00%> (ø)

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more