Migrate REST API docs previews to use reference.config.yml

Production system currently uses `reference.config.yml`, but automation generates a `mapping.json`... the mapping.json system is deprecated.

Example error that might be coming from `mapping.json` generation: https://github.com/Azure/azure-rest-api-specs-pr/pull/17939/checks?check_run_id=26243917599

Update: As @nickwalkmsft pointed out below, this is not the cause of the failure linked above. The reason for that particular failure was because of the additions of two new workflow files, sdk-suppressions.yaml and suppressions.yaml, being added but not excluded from the function that determines which changed files in a PR are swagger files. This issue was fixed in the openapi-apls repository by @mikeharder in this [PR](https://dev.azure.com/devdiv/DevDiv/_git/openapi-alps/pullrequest/568103).

Right now, the automation will handle both reference.config.yml and mapping.json and we should still ultimately move the REST API docs previews to use the reference.config.yaml.