Support `physical` sections in the editor

[jagoldstein]

When uploading data objects with a package and submitting, no physical section is created in the EML. Typically, this section would provide file size, checksum, and the online distribution URL.

Examples: https://test.arcticdata.io/#view/urn:uuid:d71babe1-3fe3-430c-913d-56eef00124b6 https://test.arcticdata.io/#view/urn:uuid:6de80a8a-f674-4b5d-b1ff-e9bbcea52634