fields.json

Remarks regarding the content of the fields.json file.

• CBERS (prefix cbers:) fields have been reviewed by Frederico Liporace.
• Planet (prefix pl:) is a guess until @cholmes provides a definitive list of fields for Planet.
• Microsoft (prefix msft:) is a guess until @lossyrob provides a definitive list of fields for Microsoft.
• CARD4L for SAR (prefix card4l:) only lists the fields that need metadata more than just a label. This is to keep the fields.json small for now and not bloat it with a lot of fields from an extension that is pretty unstable.
• Sentinel (prefix sentinel:) is unofficial and a compilation from things found on the web. We may remove/change the fields in the future.