Misc Updates for release 0.18.

[PaulHuwe]

Resolves RAD-nnnn

Closes #

This PR addresses schema changes needed for release 0.18.

• Adding new Dark keywords to the required list.
• Removed the truncated keyword from the GuideWindow table.

Checklist

• Schema changes discussed at RAD Review Board meeting
• Added entry in CHANGES.rst under the corresponding subsection
• Updated relevant roman_datamodels utilities and tests
• Passed romancal regression testing on Jenkins / PLWishMaster. Link: https://plwishmaster.stsci.edu:8081/job/RT/job/romancal/XXX/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

📢 Thoughts on this report? Let us know!.

[WilliamJamieson]

There are a couple of spurious change which have made it into this PR. If we want these as part of the 0.18 release, then they should be placed in a separate PR which is merged prior to this one.

[kdupriestsci]

looks ok