Callbacks service docs updated

api/edge/callbacks/internal/model/endpoint.go

@@ -0,0 +1,22 @@
+package model
+
+import (
+	"time"
+
+	"github.com/tech/sendico/pkg/db/storable"
+	pmodel "github.com/tech/sendico/pkg/model"
+)
+
+// Endpoint describes one target callback endpoint.
+type Endpoint struct {
+	storable.Base
+	pmodel.OrganizationBoundBase
+	URL            string
+	SigningMode    string
+	SecretRef      string
+	Headers        map[string]string
+	MaxAttempts    int
+	MinDelay       time.Duration
+	MaxDelay       time.Duration
+	RequestTimeout time.Duration
+}