chore: bump to php 7.4 and add ext-json

Author: Stéphane Bour

composer.json

@@ -3,8 +3,9 @@
     "description": "Wrapper for OVH APIs",
     "license": "BSD-3-Clause",
     "require": {
-        "php": ">=7.3",
-        "guzzlehttp/guzzle": "^6.0||^7.0"
+        "php": ">=7.4",
+        "guzzlehttp/guzzle": "^6.0||^7.0",
+        "ext-json": "*"
     },
     "autoload": {
         "psr-4": {"Ovh\\": "src/"}