Use GBFS 3 manifest for feed discovery in rental service directory

[testower]

Summary

THIS IS A BREAKING CHANGE.

Changes the vehiclerentalservicedirectory sandbox to use the manifest.json file from GBFS v3 as a way to discover available GBFS feeds. The manifest.json file can either be fetched from a remote server or served as a file on the local file system.

If multiple GBFS versions are available for a specific feed / system, we will choose the latest available (and supported) version.

Issue

Continuation of #6735 and related to #6708

Unit tests

This sandbox doesn't have tests. Tested manually.

Documentation

The documentation was updated.

Changelog

Do we use changelogs for sandbox code?

[codecov]

Codecov Report

❌ Patch coverage is 11.11111% with 48 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.09%. Comparing base (cc6c6c6) to head (8ea3513).
⚠️ Report is 280 commits behind head on dev-2.x.

Files with missing lines	Patch %	Lines
...irectory/VehicleRentalServiceDirectoryFetcher.java	0.00%	48 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             dev-2.x    #6900      +/-   ##
=============================================
- Coverage      72.10%   72.09%   -0.02%     
  Complexity     19660    19660              
=============================================
  Files           2124     2124              
  Lines          79507    79503       -4     
  Branches        8050     8050              
=============================================
- Hits           57326    57314      -12     
- Misses         19344    19353       +9     
+ Partials        2837     2836       -1     

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[leonardehrenfried]

This satisfies the sandbox contract and I cannot see anything malicious in it.

@hbruch, the only other known user of this sandbox feature, has said he is fine with this change.

[vpaturet]

I would not skip the changelog for this PR