Describe the purpose of your pull request

This PR fixes two issues related to Unity WebGL:

• Fix a regression that breaks config fetching in Unity WebGL when external cache is used.
• Fix the UnityWebGL sample script to not cause unnecessary CORS OPTIONS requests.

Related issues (only if applicable)

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How to test? (only if applicable)

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Security (only if applicable)

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Requirement checklist (only if applicable)

• I have covered the applied changes with automated tests.
• I have executed the full automated test set against my changes.
• I have validated my changes against all supported platform versions.
• I have read and accepted the contribution agreement.