Import `.oore.yaml` into pipeline settings

Reads a `version: 2` `.oore.yaml` back into the pipeline's form settings: the inverse of the export. The file is validated as `oore pipeline validate` does. Settings are returned only when the form can hold the whole file; exported again, they plan the same as the file. Everything else is listed in `unsupported`. Nothing is saved, and secret references stay as written.

curl -X POST "https://example.com/v1/pipelines/import-yaml" \  -H "Content-Type: application/json" \  -d '{    "yaml": "string"  }'

{  "errors": [    "string"  ],  "execution_config": null,  "google_play": null,  "notes": [    "string"  ],  "representable": true,  "testflight_group": "string",  "trigger_config": null,  "unsupported": [    "string"  ],  "valid": true}