updating builder image to use JDK21 based image

Updating builder image to UBI9 JDK21 Image
and removing the references to
install maven externally

Dockerfile

@@ -1,17 +1,14 @@
 # This Dockerfile is intended for use by openshift/ci-operator config files defined
 # in openshift/release for v4.x prow based PR CI jobs
 
-FROM quay.io/openshift/origin-jenkins-agent-maven:4.11.0 AS builder
+FROM registry.access.redhat.com/ubi9/openjdk-21:1.20 AS builder
 WORKDIR /java/src/github.com/openshift/jenkins-client-plugin
 COPY . .
 USER 0
-# We need a newer maven version as the RHEL package is still on 3.6.2
-RUN curl -L -o maven.tar.gz https://dlcdn.apache.org/maven/maven-3/3.8.8/binaries/apache-maven-3.8.8-bin.tar.gz && \
-	mkdir maven && \
-	tar -xvzf maven.tar.gz -C maven --strip-component 1
+
 # Use the downloaded version of maven to build the package
-RUN ./maven/bin/mvn --version && \
-	./maven/bin/mvn clean package
+RUN mvn --version
+RUN mvn clean package
 
 FROM registry.ci.openshift.org/origin/4.16:jenkins
 RUN rm /opt/openshift/plugins/openshift-client.jpi