Add CI check to prevent API documentation drift

https://github.com/GSA/touchpoints/pull/2085 added Rswag as a tool to generate API documentation. That PR originally included a new CI step that ran the Rswag script to generate `public/api/v1/openapi.yml` and failed the build if the CI-generated file did not match the versioned file in the repo. This was to check that developers are re-running the API generation script before commits so the spec does not drift from the actual API.

The step looked like this:
```
# Verify the committed OpenAPI spec is in sync with the rswag request specs.
# swaggerize regenerates public/api/v1/openapi.yml from spec/requests/api/**;
# if the result differs from what is committed, the spec has drifted and the
# build fails. Runs the full (unsplit) rswag suite on one container only so the
# generated spec is complete.
- run:
name: Verify OpenAPI spec is up to date
command: |
if [ "$CIRCLE_NODE_INDEX" != "0" ]; then
echo "Skipping OpenAPI sync check on parallel container $CIRCLE_NODE_INDEX"
exit 0
fi
set -euo pipefail
# RSWAG_DRY_RUN=0 is required so rswag runs the request examples and
# the after-callbacks that capture response bodies as OpenAPI examples.
# --dry-run is enabled by default on RSpec 3, which would skip them.
RSWAG_DRY_RUN=0 bundle exec rake rswag:specs:swaggerize
if ! git diff --exit-code -- public/api/v1/openapi.yml; then
echo "ERROR: public/api/v1/openapi.yml is out of date."
echo "Run 'RSWAG_DRY_RUN=0 bundle exec rake rswag:specs:swaggerize' locally and commit the result."
exit 1
fi
echo "OpenAPI spec is up to date."
```

This check kept failing because of minor whitespace changes between the YAML file generated on my computer vs the YAML file generated on the CI server. I removed the check to get the PR merged. This ticket is a follow-up to figure out the right way to deal with machine-specific YAML formatting, so that the CI check can be added back in.

Start with the Rswag generation command, public/api/v1/openapi.yml, and the request specs under spec/requests/api/**. Run RSWAG_DRY_RUN=0 bundle exec rake rswag:specs:swaggerize locally and compare its output with CI-generated output to identify machine-specific formatting. Done means a reliable comparison approach is defined and the CI drift check can be restored without false failures.

Written by the indexing model from the issue text.