Implement FAIRiCat for API discovery

[slint]

FAIRiCat, is a simple specification that allows web services to declare what commonly known APIs they support (e.g. OAI-PMH, FAIR Signposting, IIIF, etc.) using a JSON file exposed under /.well-known/api-catalog.

For InvenioRDM, to describe the following services/APIs:

• OAI-PMH
• IIIF
• Sitemaps
• Robots.tx

we would serve the following file:

{
  "linkset": [
    {
      "anchor": "https://inveniordm.web.cern.ch/oai2d",
      "service-doc": [
        {
          "href": "https://www.openarchives.org/OAI/openarchivesprotocol.html",
          "type": "text/html",
          "title": "Open Archives Initiative - Protocol for Metadata Harvesting - v.2.0"
        }
      ],
      "service-meta": [
        {
          "href": "https://inveniordm.web.cern.ch/oai2d?verb=Identify",
          "type": "application/xml"
        }
      ]
    },
    {
      "anchor": "https://inveniordm.web.cern.ch/api/iiif",
      "service-doc": [
        {
          "href": "https://iiif.io/api/presentation/3.0/",
          "type": "text/html",
          "title": "Presentation API 3.0 —  IIIF | International Image Interoperability Framework"
        }
      ]
    },
    {
      "anchor": "https://inveniordm.web.cern.ch/sitemap.xml",
      "service-doc": [
        {
          "href": "https://www.sitemaps.org/protocol.html",
          "type": "text/html",
          "title": "sitemaps.org - Protocol"
        }
      ]
    },
    {
      "anchor": "https://inveniordm.web.cern.ch/robots.txt",
      "service-doc": [
        {
          "href": "https://datatracker.ietf.org/doc/rfc9309/",
          "type": "text/html",
          "title": "RFC 9309 - Robots Exclusion Protocol"
        }
      ]
    }
  ]
}

The file should be generated and served dynamically, since if e.g. IIIF or any of the features/APIs are disabled, they shouldn't be included in the output JSON.