Support registering multiple adjuncts in single payload

[donaldgray]

Ticket number #1073 added endpoint POST /customers/{c}/spaces/{s}/images/{i}/adjuncts to support registering a single adjunct.

This ticket is to extend that same endpoint to support registering 1:n adjuncts in a single payload, see registering multiple adjuncts documentation. From that documentation:

This POST to the asset's adjuncts collection can take a single adjunct, an array of adjuncts, or a Hydra Collection with an array of adjuncts as member.

The following would all be equivalent, examples 2 + 3 only show a single adjunct for brevity.

Single Adjunct (currently supported)

{
  "id": "mets-from-origin",
  "origin": "https://dlcs.example/mets.xml",
  "@type": "Dataset",
  "mediaType": "text/xml",
  "profile": "http://www.loc.gov/standards/alto/v3/alto.xsd",
  "label": { "en": [ "METS-ALTO XML" ] },
  "iiifLink": "seeAlso"
}

Array

[
  {
    "id": "mets-from-origin",
    "origin": "https://dlcs.example/mets.xml",
    "@type": "Dataset",
    "mediaType": "text/xml",
    "profile": "http://www.loc.gov/standards/alto/v3/alto.xsd",
    "label": { "en": [ "METS-ALTO XML" ] },
    "iiifLink": "seeAlso"
  }
]

Hydra Collection

{
  "@type": "Collection",
  "members": [
    {
      "id": "mets-from-origin",
      "origin": "https://dlcs.example/mets.xml",
      "@type": "Dataset",
      "mediaType": "text/xml",
      "profile": "http://www.loc.gov/standards/alto/v3/alto.xsd",
      "label": { "en": [ "METS-ALTO XML" ] },
      "iiifLink": "seeAlso"
    }
  ]
}

Processing of each adjunct follow rules for single (e.g. notify Engine if it has an "origin", finish in API if it's "external" etc).

• Support POSTing an array of adjuncts
• Support POSTing an Hydra Collection of adjuncts
• Return 200 if overall save succeeds, or 4xx/5xx if at least one fails
  • If possible avoid partial failures - strive for full success or failure (to discuss)
• Return a Hydra Collection of adjuncts, regardless of the format of the body