Add initial tests cases for B15.0 (repo v15.2.0)

[rchenatjpl]

🗒️ Summary

https://nasa-pds.github.io/releases/15.0/rdd.html has 4 I&T issues for pds4-information-model. These files test 3 of them: 794, 795 (2parts), 797. 801 needs no testing.

⚙️ Test Data and/or Report

One of the following should be included here:

• Reference to regression test included in code (preferred wherever reasonable)
• Attach test data here + outputs of tests

♻️ Related Issues

[jordanpadams]

Tests fails, but they shouldn't, so merging to main so fixes for #819 and #820 can be easily tested with these tests.