entc/gen/template: improve goimports time by adding missing imports (#4103)

entc/gen/template/dialect/sql/entql.tmpl

@@ -12,6 +12,9 @@ in the LICENSE file in the root directory of this source tree.
 {{ template "header" $ }}
 
 import (
+	"context"
+	"time"
+
 	"{{ $.Config.Package }}/predicate"
 	{{- range $n := $.Nodes }}
 		{{ $n.PackageAlias }} "{{ $.Config.Package }}/{{ $n.PackageDir }}"