feat(plugin): support fluentd loki output

[fatpa]

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #310

Does this PR introduced a user-facing change?

None

Additional documentation, usage docs, etc.:

apiVersion: fluentd.fluent.io/v1alpha1
kind: ClusterOutput
metadata:
  name: fluentd-output-loki
  labels:
    output.fluentd.fluent.io/enabled: "true"
spec: 
  outputs: 
  - loki:
      host: loki-logging-data.kubesphere-logging-system.svc
      port: 3100

[benjaminhuo]

@fatpa Thanks for the contribution!
Would you sign your commit as below?

git commit -s --amend
git push -f

Thanks!

[fatpa]

@fatpa Thanks for the contribution! Would you sign your commit as below?

git commit -s --amend
git push -f

Thanks!

Of course. Done.

[wenchajun]

As far as I know, the fluentd image doesn't have the loki plugin built in, so we should modify this dockerfile file.
https://github.com/fluent/fluent-operator/blob/master/cmd/fluent-watcher/fluentd/Dockerfile.amd64#L38

[wanjunlei]

Why add a new TLS plugin in apis/fluentd/v1alpha1/plugins, we should use the TLS plugin in apis/fluentbit/v1alpha2/plugins.

in addition, we should move the TLS, ConfigMapLoader, and SecretLoader to a new package to avoid duplicate definitions.

[fatpa]

Why add a new TLS plugin in apis/fluentd/v1alpha1/plugins, we should use the TLS plugin in apis/fluentbit/v1alpha2/plugins.

in addition, we should move the TLS, ConfigMapLoader, and SecretLoader to a new package to avoid duplicate definitions.

Just follow the current design for the apis/fluentd and avoid the differences between fluentd and fluentbit.
I also think the common package is the best to avoid duplicate definitions, and we should create one more PR for it, instead of this one.

[fatpa]

As far as I know, the fluentd image doesn't have the loki plugin built in, so we should modify this dockerfile file. https://github.com/fluent/fluent-operator/blob/master/cmd/fluent-watcher/fluentd/Dockerfile.amd64#L38

I will add it.

[benjaminhuo]

Why add a new TLS plugin in apis/fluentd/v1alpha1/plugins, we should use the TLS plugin in apis/fluentbit/v1alpha2/plugins.

in addition, we should move the TLS, ConfigMapLoader, and SecretLoader to a new package to avoid duplicate definitions.

@wenchajun You can create another PR to move tls to a common place

[benjaminhuo]

@fatpa Thanks very much for the contribution!

[benjaminhuo]

@fatpa Would you please create another PR to add docs to the Fluentd Loki plugin as https://github.com/fluent/fluent-operator/blob/master/docs/plugins/fluentd/index.md ?

Thanks
Benjamin

[fatpa]

Sure. I will make it in a few days.