Update middleware to validate incoming request from Discord Service

[joyguptaa]

Description:

The current middleware verifyDiscordBot requires an update to properly validate incoming requests from the Discord service. Right now, it partially handles this by checking the x-service-name header and verifying the token, but lacks complete validation logic specific to Discord's expected signature-based request validation (if applicable).

Proposed Changes:

• Ensure the middleware performs complete validation of incoming requests from Discord, including:
• Verifying the authorization header format.
• Confirming x-service-name equals DISCORD_SERVICE.
• If x-service-name is DISCORD_SERVICE, ensure botVerification.verifyDiscordService(token) returns a valid result and implements any additional checks Discord requires (e.g., signature verification).
• Maintain compatibility with existing token-based validation from Cloudflare Worker (CLOUDFLARE_WORKER).
• Improve error handling and response messages for clarity.