ISSUE-9249: Upgrade Netty dependency in broker to solve vulnerabilities: CVE-2019-16869, CVE-2020-11612, CVE-2019-20445, CVE-2019-20444

[sijie]

Original Issue: apache#9249

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Version of Netty (4.1.32) used inside Apache Pulsar Broker (at least 2.7.0) is affected by following high risk vulnerabilities: CVE-2019-16869, CVE-2020-11612, CVE-2019-20445, CVE-2019-20444.

All these vulnerabilities are solved in Netty 4.1.46.Final.

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