feat(build): deploy to maven.codelibs.org

[marevol]

Summary

Publish this plugin through maven.codelibs.org instead of Maven Central, matching the distribution the Fess plugins already use.

pom.xml

• Add the wagon-ssh-external build extension, which provides the scpexe:// transport. It drives the external ssh and scp commands rather than an embedded SSH client, so key handling follows the system OpenSSH configuration. The embedded alternative, wagon-ssh, depends on com.jcraft:jsch 0.1.55, whose only key types are DSA, ECDSA, RSA and PKCS8.
• Add distributionManagement for the CodeLibs release and snapshot repositories, and resolve dependencies from them.
• Remove central-publishing-maven-plugin. Its DeployLifecycleParticipant disables maven-deploy-plugin, so leaving it in place would prevent deployment entirely.
• Declare maven-release-plugin with releaseProfiles=release and move maven-gpg-plugin into that profile. Ordinary builds no longer need a GPG key, while release:perform still signs the artifacts.

README.md

Install from a URL instead of Maven coordinates. The opensearch-plugin installer resolves the group:artifact:version form against repo1.maven.org only, so that form no longer works for this plugin. Version 3.8.0 and earlier remain available on Maven Central.

Verification

• mvn clean deploy -DskipTests -DaltDeploymentRepository=... deploys the jar, sources, javadoc and plugin zip, confirming maven-deploy-plugin is no longer disabled.
• mvn help:effective-pom shows maven-gpg-plugin in build/plugins only when -Prelease is given.
• mvn test passes.