Support downloads where tract, patch and object id are not present in the catalog.

[aritraghsh09]

Feature request

• It is not uncommon for astronomers to only have RA/DEC positions available for a download (without any information on tract, patch, or object id).
• The downloader should be able to skip the sort step in these situations and send requests to the HSC service only with RA, DEC positions.
• We should warn the user that having the tract, patch info will speed up the download.
• If the user does not provide any object_ids, we should say that we will just return the order in the list (0,1,2,3...) as the object ID in the manifest.

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• I have described the purpose of the suggested change, specifying what I need the enhancement to accomplish, i.e. what problem it solves.
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[mtauraso]

This may very nearly work already. Rects are dataclasses and though tract is part of the sort, its perfectly valid to make a bunch of Rects with tract=None and they will sort just fine.

Probably this will have issues in the downloader because of the hardcoded list of fields that includes tract and that is what will need to be worked around.

object_ids I'm less sure of, but we might be able to work without them.