Add "Gradle Wrapper Validation" plugin (#3435)

This Woodpecker CI plugin validates the checksums of all Gradle Wrapper
JAR files present in the repository and fails if any unknown Gradle
Wrapper JAR files are found. It is a port of
[gradle/wrapper-validation-action](https://github.com/gradle/wrapper-validation-action).

docs/plugins/woodpecker-plugins/plugins.json

@@ -179,6 +179,11 @@
       "name": "Kaniko",
       "docs": "https://raw.githubusercontent.com/woodpecker-ci/plugin-kaniko/main/docs.md",
       "verified": true
+    },
+    {
+      "name": "Gradle Wrapper Validation",
+      "docs": "https://codeberg.org/beaks/gradle-wrapper-validation/raw/branch/main/docs.md",
+      "verified": false
     }
   ]
 }