feat(12.2-02): add the fileupload field with deferred uploads committed on save

- type: fileupload compiles the D-08 keys and binds to the model's attach.Relation at boot
- X-Session-Key (cabana.SessionKeyHeader) carries the form session key; RecordInput.SessionKey
- GET and POST .../{id}/files/{field}: list with pending uploads, multipart upload into attach.Store
- the create and update save attaches the session's pending files in its transaction
- swagger2openapi folds formData parameters into a multipart requestBody
- admin OpenAPI, TS types, conformance cases, README and forms docs

modules/cabana/settings.go

@@ -63,7 +63,7 @@ func compileSetting(pluginID string, item pact.SettingsItem, fsys fs.FS) (*Compi
 	}
 	for _, field := range fields {
 		// A settings screen has no admin controller to own actions or view models.
-		if field.Type == "widget" || field.Type == "partial" {
+		if field.Type == "widget" || field.Type == "partial" || field.Type == "fileupload" {
 			return nil, fmt.Errorf("cabana: setting %s field %s: type %s is not supported on a settings form", item.Code, field.Name, field.Type)
 		}
 	}