[build] Check Matrix github action

This Action performs tests (clean check) in all three OS using NIO,
plus an additional run with epoll on Linux and an additional run with
KQueue on OSX.

It replaces the former Java CI action.

.github/workflows/check_transport.yml

@@ -0,0 +1,28 @@
+name: Check Matrix
+
+on: [push, pull_request]
+
+jobs:
+  build:
+
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macOS-latest, windows-latest]
+        transport: [native, nio]
+        exclude:
+          # excludes native on Windows (there's none)
+          - os: windows-latest
+            transport: native
+
+    steps:
+    - uses: actions/checkout@v1
+    - name: Set up JDK 1.8
+      uses: actions/setup-java@v1
+      with:
+        java-version: 1.8
+    - name: Build with Gradle
+# IF WE NEED TO TEST DIFFERENT VERSIONS OF NETTY, WE CAN ADD forceNettyVersion TO THE MATRIX
+#      run: ./gradlew check -PforceTransport=${{ matrix.transport }} -PforceNettyVersion=${{ matrix.netty }}
+      run: ./gradlew clean check -PforceTransport=${{ matrix.transport }}