Recognize music with an agent's prepaid key

Same parameters and response as the standard endpoint (POST / on api.audd.io), with the agent key as Authorization: Bearer instead of api_token. One credit per request when recognition gave an answer (a match or a no-match) or failed with AudD error 300 (the audio couldn't be fingerprinted) or 19 (internal error). Free: every other error answer, including input errors (no file, a URL that could not be downloaded, unsupported or undecodable audio, a file over 15 MB), unknown errors (100), timeouts and crashes on our side. With a balance of 0 the answer is 402 with a challenge for one pack; pay it and repeat the same request. Audio file up to 15 MB, as a multipart upload or base64 in the audio parameter (a larger file gets AudD error 400, which is free). The whole request body may be up to 24 MB. Guide: https://audd.io/auth.md