Include whitelisted HTTP headers in the extended_unique_key computation

[vdusek]

• Modify the extended_unique_key computation to include a set of predefined HTTP headers, alongside the existing normalized URL and payload.
• Only include headers from the whitelist.
• Identify which headers should be included, such as Accept, Accept-Language, Authorization, and others that may affect request outcomes.
• See the issue Improve the deduplication of requests #178 for further context.