RFC fetcher does not process drafts IDs, because prefixedIdentifier does not begin with rfc prefix.

Example URL for draft's raw bibtex resource https://datatracker.ietf.org/doc/draft-ietf-sidrops-aspa-verification/bibtex
URL structure is the same as in RFC resource, so no change in fetching part is required.

Ref: #3971 5d23970 @jacksonrya

Thanks in advance.