worker/osbuild: use dedicated struct for GCP config internally

Previously, the internal `OSBuildJobImpl` structure defined only
`GCPCreds` member. This is not practical, once there will be more
than one GCP-related variable.

Define a new `GCPConfiguration` structure, move the credentials variable
into it and use it in `OSBuildJobImpl` instead.

cmd/osbuild-worker/jobimpl-osbuild.go

@@ -31,6 +31,10 @@ import (
 	"github.com/osbuild/osbuild-composer/internal/worker/clienterrors"
 )
 
+type GCPConfiguration struct {
+	Creds string
+}
+
 type S3Configuration struct {
 	Creds               string
 	Endpoint            string
@@ -52,7 +56,7 @@ type OSBuildJobImpl struct {
 	Store            string
 	Output           string
 	KojiServers      map[string]kojiServer
-	GCPCreds         string
+	GCPConfig        GCPConfiguration
 	AzureCreds       *azure.Credentials
 	AWSCreds         string
 	AWSBucket        string
@@ -160,9 +164,9 @@ func (impl *OSBuildJobImpl) getGCP(credentials []byte) (*gcp.GCP, error) {
 	if credentials != nil {
 		logrus.Info("[GCP] 🔑 using credentials provided with the job request")
 		return gcp.New(credentials)
-	} else if impl.GCPCreds != "" {
+	} else if impl.GCPConfig.Creds != "" {
 		logrus.Info("[GCP] 🔑 using credentials from the worker configuration")
-		return gcp.NewFromFile(impl.GCPCreds)
+		return gcp.NewFromFile(impl.GCPConfig.Creds)
 	} else {
 		logrus.Info("[GCP] 🔑 using Application Default Credentials via Google library")
 		return gcp.New(nil)

cmd/osbuild-worker/main.go

@@ -351,9 +351,9 @@ func main() {
 
 	// If the credentials are not provided in the configuration, then the
 	// worker will rely on the GCP library to authenticate using default means.
-	var gcpCredentials string
+	var gcpConfig GCPConfiguration
 	if config.GCP != nil {
-		gcpCredentials = config.GCP.Credentials
+		gcpConfig.Creds = config.GCP.Credentials
 	}
 
 	// If the credentials are not provided in the configuration, then the
@@ -435,7 +435,7 @@ func main() {
 			Store:       store,
 			Output:      output,
 			KojiServers: kojiServers,
-			GCPCreds:    gcpCredentials,
+			GCPConfig:   gcpConfig,
 			AzureCreds:  azureCredentials,
 			AWSCreds:    awsCredentials,
 			AWSBucket:   awsBucket,