Makes Context Propagation a compile time dependency

otherwise a project needs to define the context-propagation library explicitly to the classpath if one wants to use it

Author: marcingrzejszczak

micrometer-tracing-bridges/micrometer-tracing-bridge-brave/gradle.lockfile

@@ -4,7 +4,7 @@ plugins {
 
 dependencies {
 	api 'io.micrometer:micrometer-observation'
-	implementation 'io.micrometer:context-propagation'
+	api 'io.micrometer:context-propagation'
 	api 'aopalliance:aopalliance'
 
 	// exemplars support