Improved Maven Workflow

Maven dependencies are now cached for faster build times. The cache is discarded once the pom.xml is updated.
The JAR files generated during the build are made available as workflow artifacts.

.github/workflows/maven.yml

@@ -4,14 +4,25 @@ on: [push]
 
 jobs:
   build:
-
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: Set up JDK 11
       uses: actions/setup-java@v1
       with:
         java-version: 11
+    - name: Cache Maven packages
+      uses: actions/cache@v2
+      with:
+        path: ~/.m2
+        key: ${{ runner.os }}-m2-${{ hashFiles('**/pom.xml') }}
+        restore-keys: ${{ runner.os }}-m2
     - name: Build with Maven
       run: mvn -B package --file pom.xml
+    - name: Stage build artifacts
+      run: mkdir staging && cp target/*.jar staging
+    - uses: actions/upload-artifact@v1
+      with:
+        name: envoy-client-artifacts
+        path: staging