Support PEM-PKCS#1 besides PEM-SPKI for RSA public keys #209
Description
Although the vast majority of ActivityPub software encodes RSA public keys in PEM-SPKI format, some software encodes RSA public keys in PEM-PKCS#1 format (see: fedify-dev/hollo#109 (comment)). Fedify currently only accepts PEM-SPKI format, so it needs to accept PEM-PKCS#1 format as well for better interoperability.