fix: replace two instances of "Context" by "Baggage"

The term "context" should not be used when referring to baggage, to
avoid confusion with the trace context spec. The two usages
replaced in this commit are from prehistoric times (e.g. commit 35a3034
from 2017) when baggage was still called correlation context.

baggage/HTTP_HEADER_FORMAT.md

@@ -132,7 +132,7 @@ Here is one more example where values with characters outside of the `baggage-oc
 baggage: userId=Am%C3%A9lie,serverNode=DF%2028,isProduction=false
 ```
 
-Context might be split into multiple headers:
+Baggage might be split into multiple headers:
 
 ```
 baggage: userId=alice

baggage/HTTP_HEADER_FORMAT_RATIONALE.md

@@ -6,7 +6,7 @@ This document provides a rationale for the decisions made for the `baggage` head
 
 - It should be human-readable. Cryptic headers would hide the fact of potential information disclosure.
 - It should be appendable (comma-separated) https://tools.ietf.org/html/rfc7230#page-24 so nodes
-can add context properties without parsing existing headers.
+can add baggage properties without parsing existing headers.
 - Keys are a single word in ASCII, and values should be a short string in UTF-8 or a derivative of a URL.
 
 ## Why a single header?