Fluentd in_tail plugin

[jjsiv]

What this PR does / why we need it:

This PR adds tail plugin to Fluentd globalInputs. It also enables setting tags for all Fluentd plugin types though I believe this has more or less no effect at the moment.

Which issue(s) this PR fixes:

Fixes #632

Does this PR introduced a user-facing change?

Users can now utilize tail input for Fluentd

Additional documentation, usage docs, etc.:

https://docs.fluentd.org/input/tail

[wenchajun]

This is actually slightly different from the first design. The question is whether to add the tail plugin to the statefulset form of fluentd, or to rewrite a controller so that fluentd is deployed as a daemonset and then configure the tail plugin for it.

[jjsiv]

I think it wouldn't be bad to have it on the statefulset as it can still be used there (although in a limited way). Obviously it would be best used on a daemonset once we have that
@benjaminhuo @wanjunlei how do you see it?

[benjaminhuo]

I think it wouldn't be bad to have it on the statefulset as it can still be used there (although in a limited way). Obviously it would be best used on a daemonset once we have that @benjaminhuo @wanjunlei how do you see it?

Agree, merge this for now