Additional support for chaining systems

Currently there is a way to chain system calls via e.g. the URL, but it is not a first class citizen.

Example "url": "https://www.secondsystem.com?firstStep=https://SESAM-SYSTEM/api"

This approach has implications when it comes to things like url-encoding, monitoring, performance and readability.

A possibility is something similar to the BizTalk pipeline implementation, to optimize common concerns without chaining micro-services in the source/sink URL config?

One could also consider a second light weight "meta pipe" that will only change "context" values, e.g. a property bag for tokens, etc. the actual data stream would pass through/remain unchanged

The  existing approach (reading a source and converting from xml to json):

{

  "_id": "acme-person-endpoint",

  "type": "pipe",

  "source": {

    "type": "dataset",

    "dataset": "global-person"

  },

  "sink": {

    "type": "json",

    "system": "xml-converter",

    "url": "/?url=http://acme-token-auth:5000/api/person"

  }

...

}

An alternative:

{

  "_id": "acme-person-endpoint",

  "type": "pipe",

  "source": {

    "type": "dataset",

    "dataset": "global-person"

  },

  "sink": {

    "type": "json",

    "system": "acme-token-auth",

    "url": "api/person",

"pipes":[

{"system-pipe": "remove-id", "sequence": 1},

{"system-pipe": "xml-converter", "sequence": 2},

{"meta-pipe": "get-token-acme-api", "sequence": 3}

]

  }

..

}