/update/json/docs should have nested document support

It is the next logical step after SOLR-6304
For the example document given below where the /orgs belong to a nested document,

{
name: 'Joe Smith',
phone: 876876687 ,
orgs :[ {name : Microsoft,
          city: "Seattle,
          zip: 98052},
        {name: Apple,
         city : Cupertino,
         zip :95014 }
      ]
} 

The extra mapping parameters would be

split=/|/orgs&
f=name:/orgs/name&
f=city:/orgs/city&
f=zip:/orgs/zip

• The objects at /org automatically becomes a child document because /org is a child path of{{/}}
• All fields falling under the /orgs/ will be mapped to the child document

alternately you can just do

split=/|/orgs&f=$FQN:/**

The fully qualified name (FQN) for chiild docs begin from /org. So the output would be

{
  "name":"Joe Smith",
  "phone":876876687,
  "_childDocuments_":[
    {
      "name":"Microsoft",
      "city":"Seattle",
      "zip":98052},
    {
      "name":"Apple",
      "city":"Cupertino",
      "zip":95014}]}