New upload target: AWS S3

Uploads an artifact to an S£ bucket and returns a presigned URL to allow
the user to download the file.

Although it uses a lot of common code with the AWS AMI upload target,
it's treated as a completely separate target.

internal/target/aws_target.go

@@ -26,3 +26,28 @@ func (AWSTargetResultOptions) isTargetResultOptions() {}
 func NewAWSTargetResult(options *AWSTargetResultOptions) *TargetResult {
 	return newTargetResult("org.osbuild.aws", options)
 }
+
+type AWSS3TargetOptions struct {
+	Filename        string `json:"filename"`
+	Region          string `json:"region"`
+	AccessKeyID     string `json:"accessKeyID"`
+	SecretAccessKey string `json:"secretAccessKey"`
+	Bucket          string `json:"bucket"`
+	Key             string `json:"key"`
+}
+
+func (AWSS3TargetOptions) isTargetOptions() {}
+
+func NewAWSS3Target(options *AWSS3TargetOptions) *Target {
+	return newTarget("org.osbuild.aws.s3", options)
+}
+
+type AWSS3TargetResultOptions struct {
+	URL string `json:"url"`
+}
+
+func (AWSS3TargetResultOptions) isTargetResultOptions() {}
+
+func NewAWSS3TargetResult(options *AWSS3TargetResultOptions) *TargetResult {
+	return newTargetResult("org.osbuild.aws.s3", options)
+}

internal/target/target.go

@@ -69,6 +69,8 @@ func UnmarshalTargetOptions(targetName string, rawOptions json.RawMessage) (Targ
 		options = new(AzureTargetOptions)
 	case "org.osbuild.aws":
 		options = new(AWSTargetOptions)
+	case "org.osbuild.aws.s3":
+		options = new(AWSS3TargetOptions)
 	case "org.osbuild.gcp":
 		options = new(GCPTargetOptions)
 	case "org.osbuild.azure.image":

internal/target/targetresult.go

@@ -47,6 +47,8 @@ func UnmarshalTargetResultOptions(trName string, rawOptions json.RawMessage) (Ta
 	switch trName {
 	case "org.osbuild.aws":
 		options = new(AWSTargetResultOptions)
+	case "org.osbuild.aws.s3":
+		options = new(AWSS3TargetResultOptions)
 	case "org.osbuild.gcp":
 		options = new(GCPTargetResultOptions)
 	case "org.osbuild.azure.image":