Configure EclipseLink for automatic schema migration

[eric-maynard]

Description

After #438 , it was reported that users with an existing metastore might not see the new columns get added to the metastore. This PR configures EclipseLink (via the default persistence.xml) to automatically add new columns when they should appear in the metastore.

Fixes #450

Type of change

Please delete options that are not relevant.

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] Documentation update
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

How Has This Been Tested?

With this PR, I have walked through the steps described in #450, and tests are now (mostly) passing:

git checkout e232b000760da335721e9112f9d52fe041289613
rm -rf extension/persistence/eclipselink/build
./gradlew :polaris-eclipselink:test --rerun
git checkout issue-450
./gradlew :polaris-eclipselink:test --rerun