Replace golang.org/x/exp with stdlib (#2857)

* Replace `golang.org/x/exp` with stdlib

These experimental packages are now available in the Go standard
library since Go 1.21.

	1. golang.org/x/exp/slices -> slices [1]
	2. golang.org/x/exp/maps -> maps [2]

[1]: https://go.dev/doc/go1.21#slices
[2]: https://go.dev/doc/go1.21#maps

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

* Run go mod tidy

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

---------

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>
Co-authored-by: Felix Kunde <felix-kunde@gmx.de>

pkg/cluster/sync.go

@@ -4,8 +4,10 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"maps"
 	"reflect"
 	"regexp"
+	"slices"
 	"strconv"
 	"strings"
 	"time"
@@ -15,8 +17,6 @@ import (
 	"github.com/zalando/postgres-operator/pkg/util"
 	"github.com/zalando/postgres-operator/pkg/util/constants"
 	"github.com/zalando/postgres-operator/pkg/util/k8sutil"
-	"golang.org/x/exp/maps"
-	"golang.org/x/exp/slices"
 	batchv1 "k8s.io/api/batch/v1"
 	v1 "k8s.io/api/core/v1"
 	policyv1 "k8s.io/api/policy/v1"