Add support for filter plugins

[theMagicalKarp]

No description provided.

[edsiper]

why do you need Go filters ?

Actually the context transition from C -> Go runtime is very expensive, filtering needs to happen as fast as possible, we offer Lua for filtering which is really fast. Is there anything that Lua cannot offer but can be done in Go ?

[theMagicalKarp]

I'd like to switch to fluent-bit and port our internal fluentd filter plugins.

In my opinion, It's more a matter of convenience than performance. The teams I work on are a lot more comfortable with using Go over C or Lua. (Which is what I thought the purpose of this repo was?)

When you say it's expensive, can you explain why that is? What's the order of magnitude?

Also seems like this is dependent on this change. fluent/fluent-bit#1277

[ericmillin]

I think WASM support will cover this case. Compile your Go to WASM and you're good to Go ;)