Publish Parent POM during release (#522)

While publishing the artifact the POM references the parent POM. However, the parent POM is not being published.

This causes problems for people using Maven/Gradle to resolve the artifact - very common for people using `job-dsl-plugin` or `gradle-jpi-plugin`.

This change publishes the parent POM so those users can get dependency resolution to work.

Fixes #373
Fixes JENKINS-43171

.github/workflows/main.yaml

@@ -95,3 +95,8 @@ jobs:
             -Dfile=build-monitor-plugin/target/build-monitor-plugin.hpi \
             -DrepositoryId=repo.jenkins-ci.org \
             -Durl=https://repo.jenkins-ci.org/releases/
+          mvn --batch-mode deploy:deploy-file \
+            -DpomFile=pom.xml \
+            -Dfile=pom.xml \
+            -DrepositoryId=repo.jenkins-ci.org \
+            -Durl=https://repo.jenkins-ci.org/releases/