Ignore Netty 4.2 dependency update suggestions

[kevinherron]

Summary

Keep weekly dependency update reports on the Netty 4.1.x train by filtering Netty 4.2+ candidates from the versions plugin output.

• Adds a versions-maven-plugin rule scoped to io.netty so the policy applies only to Netty dependency suggestions.
• Ignores Netty versions in [4.2.0,), keeping 4.1.x patch updates visible while suppressing 4.2.x suggestions.

Key Changes

• Netty update policy: The versions plugin rule set now includes a group-specific ignore range for io.netty, preserving the existing prerelease filtering while preventing major/minor train jumps into 4.2.x.

Testing

• mvn versions:display-dependency-updates - passed; visible Netty suggestions stayed on 4.1.x (4.1.133.Final -> 4.1.135.Final) with no 4.2.x candidates.
• mvn -q spotless:apply - passed.
• mvn -q clean compile - passed.
• Preflight review: APPROVED.