JP-3327: Modify mirmrsptcorr data model

[drlaw1558]

Implements the data model changes described by https://jira.stsci.edu/browse/CRDS-721

Checklist

• [x] added entry in CHANGES.rst (either in Bug Fixes or Changes to API)
• [ ] updated relevant tests
• [ ] updated relevant documentation
• [ ] updated relevant milestone(s)
• [x] added relevant label(s)

[codecov[bot]]

Codecov Report

Patch has no changes to coverable lines.

Files Changed	Coverage
src/stdatamodels/jwst/datamodels/mrsptcorr.py	ø

:loudspeaker: Thoughts on this report? Let us know!.

[hbushouse]

Started a regtest run, pointing to this PR commit, at https://plwishmaster.stsci.edu:8081/job/RT/job/JWST-Developers-Pull-Requests/905

[hbushouse]

Regression test run was clean. I'm merging.