Ensure most recent metadata is served despite duplicate version 0's

[jphui]

Checklist

• The PR conforms to DataHub's Contributing Guideline (particularly Commit Message Format)
• Links to related issues (if applicable)
• Tests for the changes have been added/updated (if applicable)
• Docs related to the changes have been added/updated (if applicable)

<fix> : added ordering to get() make sure that the most recent record (despite duplicates in other versioning) is at the top and returned

<test> : added a unit test with corresponding SQL script to ensure that the above fix works

The unit test requires a new script because the existing scripts would throw a Primary / Unique Key Error; a new script that adds createdOn was required.

[yangyangv2]

several comments

[yangyangv2]

I think this needs to be inside the For loop. Basically you want

//   SELECT * FROM metadata_aspect WHERE urn = 'urn0' AND aspect = 'aspect0' AND version = 0 ORDER BY createdOn DESC limit 1
//   UNION ALL
//   SELECT * FROM metadata_aspect WHERE urn = 'urn0' AND aspect = 'aspect1' AND version = 0 ORDER BY createdOn DESC limit 1

does it make sense?

[jphui]

I thought through this as well and believed it should be outside because in the case where you're running multiple SELECT's, we want the final result to be ordered, not just each subsection.