fix: print username for maven repo publish and revert maven-source-plugin to 3.2.1 (#307)

* fix: update release pipeline to use maven token instead of user:password

* fix:revert maven-source-plugin to 3.2.1

* fix: print username for maven repo publish and revert
maven-source-plugin to 3.2.1

Author: dixuswe

.kokoro/release.sh

@@ -19,6 +19,7 @@ setup_environment_secrets() {
   export SONATYPE_USERNAME=$(cat ${KOKORO_KEYSTORE_DIR}/75669_functions-framework-java-release-bot-sonatype-password | cut -f1 -d':')
   export SONATYPE_PASSWORD=$(cat ${KOKORO_KEYSTORE_DIR}/75669_functions-framework-java-release-bot-sonatype-password | cut -f2 -d':')
   export GPG_PASSPHRASE=$(cat ${KOKORO_KEYSTORE_DIR}/70247_maven-gpg-passphrase)
+  echo $SONATYPE_USERNAME
 
   # Add the key ring files to $GNUPGHOME to verify the GPG credentials.
   export GNUPGHOME=/tmp/gpg

functions-framework-api/pom.xml

@@ -73,7 +73,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-source-plugin</artifactId>
-        <version>3.3.1</version>
+        <version>3.2.1</version>
         <executions>
           <execution>
             <id>attach-sources</id>