Feature/support nested fields

[Danny02]

Hi,

this PR contains features I added to a private fork of this repo. I want to give you the oppertunity to upstream them if you are interested.

P.S. I needed to add Local.ROOT to the money conversion or the tests would fail on my machine (numbers are formatted like 1,000.34 instead of 1.000,34 in Germany)

Background

I'm working with complex JSON data and I want to optimize the Elastic indices I create from my Kafka data. I have a single source topic and want to create several output indicies in Elastic to optimize for search patterns we have.

{
  "baseData": {
    "country": "DE"
   }
}

I want to create an index named src-topic-DE

[jeqo]

Thanks @Danny02. Appreciate this contribution.
Regarding nested fields, we are on-hold of KIP-821 being implemented, as it should provide a common way to deal with nested fields in SMTs.
Though, we are not sure when is this going to be released. So, in the meantime, will leave this PR as open -- and dive back if we see KIP-821 is not moving forward and need to reassess this feature.
Thanks again!