feat(CI): move from Travis to GitHub Actions

original workflow by Helias
git apply actions by locus313

Co-Authored-By: Stefano Borzì <stefanoborzi32@gmail.com>

.github/workflows/core-build.yml

@@ -0,0 +1,50 @@
+name: core-build
+on:
+  push:
+  pull_request:
+
+jobs:
+  build:
+    strategy:
+      fail-fast: false
+      matrix:
+        compiler: [clang6, clang9, clang10]
+    runs-on: ubuntu-20.04
+    name: ${{ matrix.compiler }}
+    env:
+      COMPILER: ${{ matrix.compiler }}
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          repository: 'azerothcore/azerothcore-wotlk'
+          ref: 'master'
+          submodules: 'recursive'
+      - uses: actions/checkout@v2
+        with:
+          submodules: 'recursive'
+          path: 'modules/mod-solo-lfg'
+      - name: Apply core patch
+        run: git apply modules/mod-solo-lfg/lfg-solo.patch
+      - name: Apply docker patch
+        working-directory: ./modules/mod-solo-lfg
+        run: git apply docker.patch        
+      - name: Cache
+        uses: actions/cache@v1.1.2
+        with:
+          path: /home/runner/.ccache
+          key: ccache:${{ matrix.compiler }}:${{ github.ref }}:${{ github.sha }}
+          restore-keys: |
+            ccache:${{ matrix.compiler }}:${{ github.ref }}
+            ccache:${{ matrix.compiler }}
+      - name: Configure OS
+        run: source ./apps/ci/ci-install.sh
+        env:
+          CONTINUOUS_INTEGRATION: true
+      - name: Import db
+        run: source ./apps/ci/ci-import-db.sh
+      - name: Build
+        run: source ./apps/ci/ci-compile.sh
+      - name: Dry run
+        run: source ./apps/ci/ci-worldserver-dry-run.sh
+      - name: Check startup errors
+        run: source ./apps/ci/ci-error-check.sh