Add github action for continuous build task for fuzzing

The continuous build task causes a build to be triggered and uploaded as a GitHub Actions artifact whenever a new push is done to main/default branch.

Continuous builds are used when a crash is found during PR fuzzing to determine whether the crash was newly introduced. If the crash is not novel, PR fuzzing will not report it. This means that there will be fewer unrelated failures when running code change fuzzing.

.github/workflows/cflite_build.yml:

+name: ClusterFuzzLite continuous builds
+on:
+  push:
+    branches:
+      - master
+permissions: read-all
+jobs:
+  Build:
+   runs-on: ubuntu-latest
+   concurrency:
+     group: ${{ github.workflow }}-${{ matrix.sanitizer }}-${{ github.ref }}
+     cancel-in-progress: true
+   strategy:
+     fail-fast: false
+     matrix:
+        sanitizer:
+        - address
+        - undefined
+        - memory
+   steps:
+   - name: Build Fuzzers (${{ matrix.sanitizer }})
+     id: build
+     uses: google/clusterfuzzlite/actions/build_fuzzers@v1
+     with:
+        language: c
+        sanitizer: ${{ matrix.sanitizer }}
+        upload-build: true
+