Support pluggable authorization mechansim

[sijie]

Currently pulsar only supports pluggable authentication mechanisms. It doesn't support pluggable authorization provides. It would be good to make this also pluggable, so users can easily integrate with their own authorization infrastructures.

[rdhabalia]

We have also seen this requirement when user wants to deploy proxy and websocket-proxy by themselves and they want to implement auth&auth which requires pluggable authorization. If it's fine then I can take it up and will create a PR.??

[merlimat]

Yep, go for it

[merlimat]

I had it marked to 2.0, but if you think you can do that for 1.22, the better

[sijie]

This is fixed by #1200