[release/v1.20.x] Prepare release 1.20.0 (#604)

Prepare release 1.20.0.

Author: opentelemetrybot

CHANGELOG.md

@@ -1,6 +1,6 @@
 # Changelog
 
-## Unreleased
+## Version 1.20.0 (2022-11-17)
 
 ### AWS X-Ray propagator
 

version.gradle.kts

@@ -1,5 +1,5 @@
-val stableVersion = "1.20.0-SNAPSHOT"
-val alphaVersion = "1.20.0-alpha-SNAPSHOT"
+val stableVersion = "1.20.0"
+val alphaVersion = "1.20.0-alpha"
 
 allprojects {
   if (findProperty("otel.stable") != "true") {