Deprecation notice

[TomAugspurger]

This deprecates the xarray-assets extension.

The deprecation notice includes recommendations to use some other extensions and libraries that would need to exist for us to actually have an alternative (I'm not planning to work on those, but chime in here if you want to).

Closes #9

[m-mohr]

Oh, I didn't expect this to happen but I'm all for it.
Do I understand correctly that the zarr extension is still to be defined? If yes, it's potentially be a topic for the next planned STAC/ZARR sprint.

[TomAugspurger]

Do I understand correctly that the zarr extension is still to be defined?

Correct, along with updating xpystac to use it. At that point I think we'd have a clear path forward from everything offered here.

[jsignell]

Is the intention to wait to merge this until the zarr extension exists? I am seeing projects like https://github.com/EOPF-Sample-Service/xarray-eopf that are relying on this extension, so it would probably be beneficial to publicize this deprecation earlier rather than later.

[m-mohr]

From my side, we can merge already. Leaving the final decision to @TomAugspurger

[TomAugspurger]

I dislike implementing deprecations without a replacement ready to go, but that's primarily in programming languages where it's annoying to get a warning that you can't do anything about, other than silence.

I'm not sure what deprecating a STAC extension does. If it's purely informational, then I think it'd be fine to merge this as long as the deprecation notice includes a request for volunteers to implement the missing pieces.

[m-mohr]

I made it a little more clear that the extension still has to be created and that STAC is open for proposals. I think with that I'll merge.