Disable _id.path by default

[clintongormley]

If you index a document like this:

POST /test/test
{ "foo": "bar", "_id": 2 }

it will throw an exception saying:

Provided id [upGeHLkQQv-aclC7mF6EWQ] does not match the content one [2]

In other words, it is using a path for the _id field, even though we haven't specified one, and there is no way to disable this.

I think that we should only do this check if the path parameter on the _id mapping is explicitly set.

[Diolor]

Related, in 1.1.1.

If you index a document like:

POST test/test
{
  "_id": {
    "$oid": "5303daa1c36b445138605a0c"
  },
  "event_id": {
    "$oid": "537c2a0ebb20c7336f5e4aca"
  },
  "start_date": "2014-05-24T20:00:00-04:00",
  "country": "Canada"
}

The auto-generated mapping will be:

{
  "test": {
    "mappings": {
       "test": {
          "properties": {
             "$oid": {
                "type": "string"
             }
          }
       }
    }
  }
}

It will normalize the _id field and will ignore the other fields.

[clintongormley]

Closing in favour of #6730 and #9059