Add serenity-bom module for dependency version alignment

[abendt]

Summary

• Adds a serenity-bom module that publishes a Bill of Materials POM for Serenity BDD
• Includes a build-time Groovy validation script ensuring all reactor modules are listed in the BOM
• Registers serenity-bom as a module in the root pom.xml

Intended effect

Users can import the BOM in their <dependencyManagement> to align all Serenity artifact versions automatically, eliminating the need to specify <version> on each individual Serenity dependency:

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>net.serenity-bdd</groupId>
            <artifactId>serenity-bom</artifactId>
            <version>${serenity.version}</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

Relevant tickets

Closes #3720

Notes

I have also updated the github build to use the provided maven wrapper version to ensure a consistent version is used locally and on github.

Github build fails: https://github.com/serenity-bdd/serenity-core/actions/runs/22038026810/job/63674148191?pr=3721

This looks it is not related to the changes from the PR. Looks this happens after the bom module was built. In the linked job i have even excluded the bom from the build