feat: Add MySQL ent-based storage driver

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

storage/ent/postgres_test.go

@@ -20,13 +20,6 @@ const (
 	PostgresEntPasswordEnv = "DEX_POSTGRES_ENT_PASSWORD"
 )
 
-func getenv(key, defaultVal string) string {
-	if val := os.Getenv(key); val != "" {
-		return val
-	}
-	return defaultVal
-}
-
 func postgresTestConfig(host string, port uint64) *Postgres {
 	return &Postgres{
 		NetworkDB: NetworkDB{