build: switch to gradle build

Our Java projects are gradle based.

.woodpecker.yml

@@ -13,9 +13,9 @@ steps:
       - pre-commit run --all-files
   "lint:style":
     group: lint
-    image: maven:3.9.4-eclipse-temurin-17
+    image: gradle:8.4.0-jdk17
     commands:
-      - mvn spotless:check
+      - gradle spotlessCheck --no-daemon
   "lint:credentials":
     group: lint
     image: ghcr.io/gitleaks/gitleaks:latest
@@ -39,6 +39,6 @@ steps:
       - hadolint Dockerfile
   "build:java":
     group: build
-    image: gradle:8.4.0-jdk17-alpine
+    image: gradle:8.4.0-jdk17
     commands:
       - ./gradlew build