Bump netty dependencies to 4.1.62.Final

[wtlucy]

Dependabot opened a PR to update netty-codec-http2 due to a CVE in the version we consume: #16180

Edit: we'll skip 4.1.60 in favor of 4.1.61: #16417
Another edit: Netty released 4.1.62 a few hours after 4.1.61 to address a regression https://netty.io/news/2021/03/31/4-1-62-Final.html so we'll go with that one

Currently Liberty only uses Netty for its grpcClient-1.0 feature, and that code is not vulnerable per the description at GHSA-wm47-8v5p-wjpj. So we don't need an update to address the vulnerability, but regardless I'll use this issue to do the update.

This update has been blocked due to an incompatibility in gRPC with the updates made in Netty 4.1.60 - see grpc/grpc-java#7953. Fixes for that will be available in 1.35.1 and 1.36.1, so once those are released we can update these dependencies together.