Include currentBatch identifiers in manifests response

[donaldgray]

Expand the "ingesting" property returned as part of API manifest to include the current batch identifiers. This will allow consumers to independently check batch status or redirect to a UI to check progress etc.

e.g.:

{
  "ingesting": {
    "finished": 0,
    "total": 11,
    "currentBatches": [ "https://api..../batches/12345" ]
  },
}

Note that we're using "currentBatches" rather than "batches" to allow possibility for adding all batches over time (e.g. if a manifest is updated multiple times it could have "old" and current batches).

This response should be included in

• Immediate response when created
• GET response IF there is a currently ingesting batch