[RQ-1327] fix: relay authorization header in case of cross origin XHR redirects

[nafees87n]

Closes issue: #1208

📜 Summary of changes:

XMLHttpRequest builds upon Fetch. It doesn’t define its own network logic. (If we added another API that could set headers it would also end up with this behavior.)

Forwards authorization header in case of cross-origin Requestly XHR redirects

✅ Checklist:

• Make sure linting and unit tests pass.
• No install/build warnings introduced.
• Verified UI in browser.
• For UI changes, added/updated analytics events (if applicable).
• For changes in extension's code, manually tested in Chrome and Firefox.
• For changes in extension's code, both MV2 and MV3 are covered.
• Added/updated unit tests for this change.
• Raised pull request to update corresponding documentation (if already exists).

🧪 Test instructions:

🔗 Other references: