Add github workflows and funding file.

.github/FUNDING.yml

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+github: KafeinDev

.github/workflows/gradle.yml

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+name: Java CI with Gradle
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up JDK 17
+        uses: actions/setup-java@v2
+        with:
+          java-version: '17'
+          distribution: 'temurin'
+          cache: gradle
+
+      - name: Grant execute permission for gradlew
+        run: chmod +x gradlew
+
+      - name: Build with Gradle
+        run: ./gradlew shadowJar
+
+      - name: Upload build artifact
+        uses: actions/upload-artifact@v3
+        with:
+          name: plugin
+          path: bukkit/build/libs/MultiDuels-*.jar