Add collection thumbnails

Our collections currently do not have thumbnails.

Motivation

There are several reasons to add collection thumbnails

1. They make for a much nicer STAC catalog browsing experience in various clients, most notably STAC Browser
2. We would like other clients, in particular VEDA UI, to be able to load collection thumbnails from STAC instead of from their own parallel config

Example

Planetary Computer is a very nice reference for how to get the most out of STAC:

Microsoft Planetary Computer	VEDA Earthdata Dashboard

The collection thumbnail is stored as an asset:

https://planetarycomputer.microsoft.com/api/stac/v1/collections

Description

In VEDA UI, the concept of "Datasets" maps to STAC collections. It can also map to other things (e.g. CMR concepts etc.), but in the case of STAC, it's just collections.

We already have thumbnails for the Datasets in the VEDA Earthdata Dashboard, which we could just copy over:

(see png files in the config repo)

We would need to find a good place to host these thumbnails, as they are not STAC db material, I guess.

We do not want to reference VEDA UI config, because in the future VEDA UI should get them from the STAC-colocated source.

Planetary Computer has them in a dedicated object storage (blob storage in Azure in their case).

Acceptance criteria

• Decided on a place to store the thumbnails
• Copied thumbnails from veda-config
• Added thumbnail references to STAC

Start by reviewing the PNG files in the veda-config develop/datasets directory and the existing STAC collection output. Determine where the thumbnails should be hosted, copy the referenced assets, and add thumbnail references to the STAC collections. Done means the storage location is decided and clients can load the thumbnails from STAC.