ComposerAuth: Handle non base64 contents

By falling back to json verification and then using that contents, users
can use both base64 and raw json for the auth env variable.

This also introduces the first proper unit test, here's to an even
brighter future!

Author: tdgroot

composer.json

@@ -35,6 +35,11 @@
             "src/Deployer/functions.php"
         ]
     },
+    "autoload-dev": {
+        "psr-4": {
+            "Hypernode\\Deploy\\Tests\\": "tests/"
+        }
+    },
     "require-dev": {
         "phpro/grumphp-shim": "^1.13",
         "phpunit/phpunit": "^9.5",