Merge azavea/stac-ml-aoi-extension

[duckontheweb]

Opening this to bring the content from azavea/stac-ml-aoi-extension into the stac-extensions org. I have tried to leave the original content intact and make the minimum number of changes required to fit the content into the stac-extensions/template format and get the build to pass. The intention is to open issues on this repo for any additional work needed on the extension (e.g. adding examples, additional reformatting, etc.).

A couple of notes:

• @echeipesh is the owner since he made all commits to the original repo. Let me know if this should change. I'm also happy to be a co-owner or sole owner if either of those options make sense).
• Did a little work to fit the content into the template format, but more probably needs to be done. I thought it would be best to do this through issues + atomic commitsPRs rather than as part of this merge.
• Had to remove the front matter in the ADR docs to make remark happy, let me know if there's a reason that needs to be in there.

[echeipesh]

💯 thank you for pulling this into the light, everything looks good and I agree with deferring needed fix-up into followup. I fully endorse growing the owner list to people who are thinking and contributing to this spec such as yourself.

[duckontheweb]

@kbgg Thanks for catching those typos, I've fixed them in 37d7387. I think there's a good chance we'll want to re-structure that main README anyway to be more consistent with some of the other STAC Extensions, but it's good to catch these in the review anyway.