Updates to OIN metadata spec

[smit1678]

From hotosm/openaerialmap#55, there has been much discussion picking up additional metadata items that are useful for OAM and other implementations of indexing and tiling tools on top of OIN. A couple proposed updates to the metadata seem necessary based on usage as well as helping promote the tools that can be built on top of it.

Current OIN spec is:

{
    "uuid": "",
    "title": "",
    "projection": "",
    "bbox": [],
    "footprint": "",
    "gsd": ,
    "file_size": ,
    "acquisition_start": "",
    "acquisition_end": "",
    "platform": "",
    "provider": "",
    "contact": "",
    "properties": {}
}

The proposed updates include an uploaded_at and a OIN version number, oin.

OIN proposed update:

{
    "oin":"0.0.1",              # OIN version number
    "uploaded_at": "",          # Date file and metadata added to OIN bucket
    "uuid": "",
    "title": "",
    "projection": "",
    "bbox": [],
    "footprint": "",
    "gsd": ,
    "file_size": ,
    "acquisition_start": "",
    "acquisition_end": "",
    "platform": "",
    "provider": "",
    "contact": "",
    "properties": {}
}

Does this seem in line with growth of this spec? Other options or ideas here that we want to consider? There is also some other conversation in that thread around OGC EO data spec. @mojodna @cgiovando Let me know if I'm missing any part of this.

cc @openimagerynetwork/oin

[wonderchook]

I think this is useful. What if instead of "oin":"0.0.1" it might be better to say "oin-version":"0.0.1" just to make it a tiny bit more human readable.