Precent character in value must be precent-encoded

[pellared]

baggage/baggage/HTTP_HEADER_FORMAT.md

Lines 53 to 56 in ebda53c

	A value contains a string whose character encoding MUST be UTF-8 [[Encoding]].
	Any characters outside of the `baggage-octet` range of characters MUST be percent-encoded.
	Characters which are not required to be percent-encoded MAY be percent-encoded.
	Percent-encoding is defined in [[RFC3986]], Section 2.1: https://datatracker.ietf.org/doc/html/rfc3986#section-2.1.

This misses a case that precent character MUST be encoded as well.

Otherwise how we would know if %20 stands for (whitespace) or %20? %20 value must be encoded into %2520.

Found here: open-telemetry/opentelemetry-go#4756 (comment)