add maven build gitea action

.gitea/workflows/maven.yaml

@@ -0,0 +1,20 @@
+name: Gitea Actions Maven Build
+
+on:
+    push:
+        branches: ['master']
+
+jobs:
+    build:
+        runs-on: ubuntu-latest
+        steps:
+          - name: Checkout the repo
+            uses: actions/checkout@v4
+          - name: Setup JDK 21
+            uses: actions/setup-java@v4
+            with:
+               java-version: 21
+               distribution: 'temurin'
+               cache: maven
+          - name: Build with Maven
+            run: mvn -B package --file pom.xml