RAD-248: Add wfi_parallel to visit section

[PaulHuwe]

Resolves RAD-248

Closes #748

This PR adds the wfi_parallel keyword block to the observation schema.

Tasks

• Update or add relevant rad tests.
• Update relevant docstrings and / or docs/ page.
• Does this PR change any schema files?
  • Schema changes were discussed at RAD Review Board meeting.
• Does this PR change any API used downstream? (If not, label with no-changelog-entry-needed.)
  • Write news fragment(s) in changes/: echo "changed something" > changes/<PR#>.<changetype>.rst (see below for change types).
  • Start a romancal regression test (https://github.com/spacetelescope/RegressionTests/actions/workflows/romancal.yml) with this branch installed ("git+https://github.com/<fork>/rad@<branch>").
  • Update relevant roman_datamodels utilities and tests.

News fragment change types:

• changes/<PR#>.feature.rst: new feature
• changes/<PR#>.bugfix.rst: fixes an issue
• changes/<PR#>.doc.rst: documentation change
• changes/<PR#>.removal.rst: deprecation or removal of public API
• changes/<PR#>.misc.rst: infrastructure or miscellaneous change

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.36%. Comparing base (e3247f3) to head (90ced94).
⚠️ Report is 76 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #800   +/-   ##
=======================================
  Coverage   86.36%   86.36%           
=======================================
  Files          15       15           
  Lines        1137     1137           
=======================================
  Hits          982      982           
  Misses        155      155           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[jbrookens]

No changes for archive.

[schlafly]

For the romancal migration of wfi_parallel, you'll need this:

rad/latest/meta/observation.yaml

Lines 160 to 167 in e37f6a1

	visit_file_sequence:
	title: Visit File Sequence
	description: |
	The visit file sequence identifies the sequence within
	the visit file group. A value of 1 indicates a prime instrument
	exposure, and a value greater than 1 indicates a parallel
	instrument exposure. The allowed range of visit file sequence
	numbers of 1 to 5 inclusive.

From those docs, you can figure out if the observation is in a parallel mode on the basis of that 's' digit; >1 means parallel.