Add support for automatic signing style (#248)

* Reorganise export options generator and add support for automatic signing style

* Update go-xcode@v1

* Fix lint issue

* Update go-xcode@v1

* Don't set default signingStyle and destination on exportOptions

* Remove unused addSigningStyle

Author: godrei

exportoptionsgenerator/certificates.go

@@ -0,0 +1,21 @@
+package exportoptionsgenerator
+
+import "github.com/bitrise-io/go-xcode/certificateutil"
+
+// CodesignIdentityProvider can list certificate infos.
+type CodesignIdentityProvider interface {
+	ListCodesignIdentities() ([]certificateutil.CertificateInfoModel, error)
+}
+
+// LocalCodesignIdentityProvider ...
+type LocalCodesignIdentityProvider struct{}
+
+// ListCodesignIdentities ...
+func (p LocalCodesignIdentityProvider) ListCodesignIdentities() ([]certificateutil.CertificateInfoModel, error) {
+	certs, err := certificateutil.InstalledCodesigningCertificateInfos()
+	if err != nil {
+		return nil, err
+	}
+	certInfo := certificateutil.FilterValidCertificateInfos(certs)
+	return append(certInfo.ValidCertificates, certInfo.DuplicatedCertificates...), nil
+}