Update rpm.md

for error "The GPG keys listed for the "grafana" repository are already installed but they are not correct for this package."

ref #9476

Kafka alerting

Prometheus client lib support gzip by itself. Which caused the
response to be double gzipped sometimes. We should use the Grafana
middle ware instead.

closes #9464

* added images to annotation docs

* added gifs and png to annotations, minor code formatting fix in alertlist