feat: Add ent-based sqlite3 storage

Signed-off-by: m.nabokikh <maksim.nabokikh@flant.com>

storage/ent/schema/offlinesession.go

@@ -0,0 +1,46 @@
+package schema
+
+import (
+	"github.com/facebook/ent"
+	"github.com/facebook/ent/schema/field"
+)
+
+/* Original SQL table:
+create table offline_session
+(
+    user_id        text not null,
+    conn_id        text not null,
+    refresh        blob not null,
+    connector_data blob,
+    primary key (user_id, conn_id)
+);
+*/
+
+// OfflineSession holds the schema definition for the OfflineSession entity.
+type OfflineSession struct {
+	ent.Schema
+}
+
+// Fields of the OfflineSession.
+func (OfflineSession) Fields() []ent.Field {
+	return []ent.Field{
+		// Using id field here because it's impossible to create multi-key primary yet
+		field.Text("id").
+			SchemaType(textSchema).
+			NotEmpty().
+			Unique(),
+		field.Text("user_id").
+			SchemaType(textSchema).
+			NotEmpty(),
+		field.Text("conn_id").
+			SchemaType(textSchema).
+			NotEmpty(),
+		field.Bytes("refresh"),
+		field.Bytes("connector_data").Nillable().Optional(),
+	}
+}
+
+// Edges of the OfflineSession.
+func (OfflineSession) Edges() []ent.Edge {
+	return []ent.Edge{}
+}