chore: add SonarCloud CPD exclusions for unavoidable duplication

[gnodet]

Summary

Adds sonar.cpd.exclusions to the root pom.xml to exclude modules with unavoidable code duplication from SonarCloud Copy-Paste Detection (CPD).

Excluded modules:

• camel-jackson3 / camel-jackson3xml (~2,200 lines): These are forks of the Jackson v2 modules (camel-jackson / camel-jacksonxml) adapted for the Jackson 3.x API. The duplication between v2 and v3 variants is unavoidable since they target different major versions of Jackson with incompatible APIs.
• camel-test-junit6 (~4,000 lines): This is a copy of camel-test-junit5 with package renames for the JUnit 6 migration. The duplication is intentional and temporary until JUnit 5 support is eventually removed.

These exclusions should bring the new code duplication metric below the 3% quality gate threshold (currently at 5.58%).

Test plan

• Verify SonarCloud analysis passes the duplication gate on the next PR scan

Claude Code on behalf of Guillaume Nodet

[github-actions]

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