feat: adding default semgrep workflow (#23)

.github/workflows/semgrep.yml

@@ -0,0 +1,36 @@
+# Name of this GitHub Actions workflow.
+name: Semgrep
+
+on:
+  # Scan changed files in PRs (diff-aware scanning):
+  pull_request:
+    branches: ['main']
+
+  # Schedule the CI job (this method uses cron syntax):
+  schedule:
+    - cron: '0 0 * * MON-FRI'
+
+jobs:
+  semgrep:
+    # User definable name of this GitHub Actions job.
+    name: Scan
+    # If you are self-hosting, change the following `runs-on` value:
+    runs-on: ubuntu-latest
+
+    container:
+      # A Docker image with Semgrep installed. Do not change this.
+      image: returntocorp/semgrep@sha256:6c7ab81e4d1fd25a09f89f1bd52c984ce107c6ff33affef6ca3bc626a4cc479b
+
+    # Skip any PR created by dependabot to avoid permission issues:
+    if: (github.actor != 'dependabot[bot]')
+
+    steps:
+      # Fetch project source with GitHub Actions Checkout.
+      - uses: actions/checkout@f43a0e5ff2bd294095638e18286ca9a3d1956744 # v3.6.0
+      # Run the "semgrep ci" command on the command line of the docker image.
+      - run: semgrep ci
+        env:
+          # Connect to Semgrep Cloud Platform through your SEMGREP_APP_TOKEN.
+          # Generate a token from Semgrep Cloud Platform > Settings
+          # and add it to your GitHub secrets.
+          SEMGREP_APP_TOKEN: ${{ secrets.SEMGREP_APP_TOKEN }}