Replace deprecated io/ioutil with modern os/io equivalents

Replaces ioutil.ReadFile, TempDir and ReadDir calls with their Go 1.16+
replacements in os package. Removes the io/ioutil import from all
affected files.

Author: ramonskie

fixtures/util/dynatrace/main.go

@@ -3,7 +3,6 @@ package main
 import (
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
 	"log"
 	"net/http"
 	"os"
@@ -69,7 +68,7 @@ func main() {
 			json.NewEncoder(w).Encode(payload)
 
 		case "/v1/deployment/installer/agent/processmoduleconfig":
-			fakeConfig, err := ioutil.ReadFile("fake_config.json")
+			fakeConfig, err := os.ReadFile("fake_config.json")
 			if err != nil {
 				w.WriteHeader(http.StatusInternalServerError)
 				w.Write([]byte(err.Error()))

src/php/extensions/composer/composer.go

@@ -4,7 +4,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"os"
 	"os/exec"
@@ -650,7 +649,7 @@ func (e *ComposerExtension) installComposer(ctx *extensions.Context, installer *
 		fmt.Printf("-----> Installing composer %s\n", composerVersion)
 
 		// Create a temporary directory for the composer download
-		tmpDir, err := ioutil.TempDir("", "composer-install")
+		tmpDir, err := os.MkdirTemp("", "composer-install")
 		if err != nil {
 			return fmt.Errorf("failed to create temp dir: %w", err)
 		}
@@ -666,7 +665,7 @@ func (e *ComposerExtension) installComposer(ctx *extensions.Context, installer *
 		}
 
 		// Find the downloaded .phar file (e.g., composer_2.8.8_linux_noarch_cflinuxfs4_abc123.phar)
-		files, err := ioutil.ReadDir(tmpDir)
+		files, err := os.ReadDir(tmpDir)
 		if err != nil {
 			return fmt.Errorf("failed to read temp dir: %w", err)
 		}