Fix/fix grafana plugin build

[chrisdutz]

Description

There were issues with the grafana sdk which seems to have referenced a library in "latest" version. Unfortunately that library got a new major version which was API incompatible with the old, so the build broke. Explicitly pulling in the last working version resolved the problem.

This PR also updates the Netty version to a version that has resolved the CVEs that we had been getting reports for, but weren't able to fix.