TS 33.128 CR 0591 - Addition of ExternalASNType

In some cases, it is useful to send information in the original encoding instead of mapping the information into specific ASN.1 parameters. This concept is used already with the SBIType and XMLType structures. There have been multiple cases when a similar structure for sending encoded payloads that use externally defined ASN.1. This concept is also used by RAN between their various specifications. This CR proposes a solution to allow the sending of payloads encoded using external ASN.1. Additionally, in order to prevent any ambiguity and allow for the proper decoding, it is proposed to include information about the schema used to encode the data with the encoded data.