SOLR-17908 Use Java 25 in Docker image

[janhoy]

https://issues.apache.org/jira/browse/SOLR-17908

This targets Solr 10.0 docker release. Will be merged to branches main, branch_10x and branch_10_0.

This will make sure that the 10.x line of Solr releases on Docker use the latest JRE from the start.
Note that Solr 10's minimum java requirement is 21, there will be benefits down the road to be on 25.

[Copilot]

Pull Request Overview

This PR updates the Solr Docker image to use Java 25 instead of Java 21, aligning with the upgrade path for Solr 10. The change involves updating the base Docker image, hardcoding the Java version in the build script, and documenting the new configuration.

Key Changes:

• Updated Docker base image from eclipse-temurin:21-jre-noble to eclipse-temurin:25-jre-noble
• Changed Java version reference in build.gradle from dynamically reading libs.versions.java.min.get() to hardcoded '25'
• Updated documentation to reflect the new Java 25 base image

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
solr/solr-ref-guide/modules/upgrade-notes/pages/major-changes-in-solr-10.adoc	Added documentation specifying the new Docker base image version
solr/docker/build.gradle	Changed Java version from dynamic library reference to hardcoded '25'
dev-docs/gradle-help/docker.txt	Updated default base image documentation from Java 21 to Java 25

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[epugh]

LGTM.