UI: provide an API call to return importer types used in a kloset

[brmzkw]

Plakar provides an API importer-types which returns all the importer types used in a Kloset:

{"total":3,"items":[{"name":"fs"},{"name":"s3"},{"name":"sftp"}]}

We want to update the UI to provide a new dashboard, displaying a summary for each source in the Kloset. Each source should contain:

• the info about the source (importer type, origin, directory)
• the info about the latest snapshot for this source
• number of snapshots for this source

The return value should be something like:

{
  "total": 4,
  "items": [
    {
      "sources": [
        {
          "type": "fs",
          "origin": "localhost",
          "directory": "/etc"
        }
      ],
      "total_snapshots": 133,
      "<other useful info>": "...",
      "latest_snapshot": {
        "identifier": "...."
      }
    }
  ]
}

We will also need a filter on /snapshots to filter the snapshots having a given source.

Before implementing this endpoint, please let us know how you want to handle multi-sources snapshots: should we have one entry in the result, or should we duplicate the snapshots for each source?