Set single URL for part of dct_references_s

[ghukill]

Purpose and background context

It was discovered that the Aardvark format expects only a single URL for the dct_references_s key http://schema.org/url, where previously we had set this as a list of objects containing lable and URL like http://schemal.org/downloadUrl.

This changes the final structure from an array of objects:

{
    "http://schema.org/url":[ {complex object here...} ]
}

to a single string:

{
    "http://schema.org/url": "https://geodata.libraries.mit.edu/record/abc123"
}

This also updates the hostname for where this URL points back to geodata.libraries.mit.edu which is the anticipated TIMDEX UI for geo resources.

Includes new or updated dependencies?

NO

Changes expectations for external applications?

YES - Transmogrifier has an associated PR: MITLibraries/transmogrifier#118

What are the relevant tickets?

• https://mitlibraries.atlassian.net/browse/GDT-68

Developer

• All new ENV is documented in README
• All new ENV has been added to staging and production environments
• All related Jira tickets are linked in commit message(s)
• Stakeholder approval has been confirmed (or is not needed)

Code Reviewer(s)

• The commit message is clear and follows our guidelines (not just this PR message)
• There are appropriate tests covering any new functionality
• The provided documentation is sufficient for understanding any new functionality introduced
• Any manual tests have been performed and verified
• New dependencies are appropriate or there were no changes