feat: Add ent-based postgres storage

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

storage/ent/client/main.go

@@ -2,6 +2,7 @@ package client
 
 import (
 	"context"
+	"database/sql"
 	"hash"
 	"time"
 
@@ -17,7 +18,9 @@ import (
 var _ storage.Storage = (*Database)(nil)
 
 type Database struct {
-	client *db.Client
+	client    *db.Client
+	txOptions *sql.TxOptions
+
 	hasher func() hash.Hash
 }
 
@@ -44,6 +47,13 @@ func WithHasher(h func() hash.Hash) func(*Database) {
 	}
 }
 
+// WithTxIsolationLevel sets correct isolation level for database transactions.
+func WithTxIsolationLevel(level sql.IsolationLevel) func(*Database) {
+	return func(s *Database) {
+		s.txOptions = &sql.TxOptions{Isolation: level}
+	}
+}
+
 // Schema exposes migration schema to perform migrations.
 func (d *Database) Schema() *migrate.Schema {
 	return d.client.Schema
@@ -54,6 +64,11 @@ func (d *Database) Close() error {
 	return d.client.Close()
 }
 
+// BeginTx is a wrapper to begin transaction with defined options.
+func (d *Database) BeginTx(ctx context.Context) (*db.Tx, error) {
+	return d.client.BeginTx(ctx, d.txOptions)
+}
+
 // GarbageCollect removes expired entities from the database.
 func (d *Database) GarbageCollect(now time.Time) (storage.GCResult, error) {
 	result := storage.GCResult{}