Migrate from gradle to pom

[sue445]

I want to release new version, but failed...

$ ./gradlew publish
Starting a Gradle Daemon (subsequent builds will be faster)
> Task :publishMavenJpiPublicationToJenkinsRepository FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':publishMavenJpiPublicationToJenkinsRepository'.
> Failed to publish publication 'mavenJpi' to repository 'jenkins'
   > Could not PUT 'https://repo.jenkins-ci.org/releases/org/jenkins-ci/plugins/yaml-axis/0.2.3/yaml-axis-0.2.3.hpi'. Received status code 401 from server: Unauthorized

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

Deprecated Gradle features were used in this build, making it incompatible with Gradle 7.0.
Use '--warning-mode all' to show the individual deprecation warnings.
See https://docs.gradle.org/6.3/userguide/command_line_interface.html#sec:command_line_warnings

BUILD FAILED in 24s
11 actionable tasks: 4 executed, 7 up-to-date

I think credential in ~/.gradle/gradle.properties doesn't pass to publishMavenJpiPublicationToJenkinsRepository. So I migrate to pom.xml

Actually, snapshot release is successful from mvn release:perform

https://repo.jenkins-ci.org/snapshots/org/jenkins-ci/plugins/yaml-axis/0.2.3-SNAPSHOT/