feat: add rdkafka gem installation to Dockerfiles for fluent-watcher

[MioOgbeni]

What this PR does / why we need it:

Hi, I want to use Kafka FluentD plugin, but the base library ruby-kafka is deprecated, which is also not compatible with my Strimzi Kafka installation. Then I tried to use the new rdkafka part of this plugin, but it fails with the fluent-operator image because it needs to have the C rdkafka library installed as well. I tried to create my own image, but now I want to publish this fix for all users.

Which issue(s) this PR fixes:

None

Does this PR introduced a user-facing change?

- rdkafka part of fluent-plugin-kafka can be now used with fluent-operator FluentD image.

Additional documentation, usage docs, etc.:

[MioOgbeni]

Now I think everything is ready for review.

I had to add some dependencies that the rdkafka library requires during the build. All these dependencies are only in build-deps, and are removed at the end.

I also tested it from the same Dockerfile on my environment, but only for the amd64 image. Currently I am not able to run also arm64 machines for proper testing. In a few months I will have arm64 machines available and will need the Kafka plugin on them as well, so I would possibly make a fix then.

[MioOgbeni]

Force pushed only due to forgotten commit sign-off ;)

[benjaminhuo]

@MioOgbeni Thank you!