go: Evaluate the tool directive in go1.24 for managing tool dependency

[ialidzhikov]

How to categorize this issue?

/area dev-productivity
/kind enhancement

What would you like to be added:
From https://tip.golang.org/doc/go1.24#tools:

Go modules can now track executable dependencies using tool directives in go.mod. This removes the need for the previous workaround of adding tools as blank imports to a file conventionally named “tools.go”. The go tool command can now run these tools in addition to tools shipped with the Go distribution. For more information see the documentation.

With this, we could adapt all the tool dependencies we manage to the new approach:

gardener/hack/tools.go

Lines 1 to 22 in e4950e2

	//go:build tools
	// +build tools
	// SPDX-FileCopyrightText: 2024 SAP SE or an SAP affiliate company and Gardener contributors
	//
	// SPDX-License-Identifier: Apache-2.0
	// This package imports things required by build scripts, to force `go mod` to see them as dependencies
	package tools
	import (
	_ "github.com/ahmetb/gen-crd-api-reference-docs"
	_ "github.com/ironcore-dev/vgopath"
	_ "github.com/onsi/ginkgo/v2/ginkgo"
	_ "go.uber.org/mock/mockgen"
	_ "golang.org/x/tools/cmd/goimports"
	_ "k8s.io/code-generator"
	_ "k8s.io/code-generator/cmd/go-to-protobuf/protoc-gen-gogo"
	_ "k8s.io/kube-openapi/cmd/openapi-gen"
	_ "sigs.k8s.io/controller-runtime/tools/setup-envtest"
	_ "sigs.k8s.io/controller-tools/cmd/controller-gen"
	)

Why is this needed:
Use the idiomatic way of managing tool dependencies.