Endpoint to export a view of a map in a format and quality appropriate for publication

[MattBlissett]

It's currently possible to download high-resolution map tiles (and basemap tiles) and assemble a map from them, but it would be better to provide a service to do this. It could export to SVG or PDF as well as PNG.

[ManonGros]

It would be good if this function would also:

• generate a full citation with associated DOI
• have the possibility to show a legend on the map

[dnoesgaard]

We could take advantage of the derivedDataset service to create a citable DOI with all contributing datasets for maps. It would probably mean that the service would require authentication, but could still run synchronously (I think).