chore: Add MetaMask security code scanner action (#458)

Adds https://github.com/MetaMask/action-security-code-scanner to this
repository.

Author: rekmarks

.github/workflows/security-code-scanner.yml

@@ -0,0 +1,38 @@
+name: MetaMask Security Code Scanner
+
+on:
+  push:
+    branches: ['main']
+  pull_request:
+    branches: ['main']
+  workflow_call:
+    secrets:
+      SECURITY_SCAN_METRICS_TOKEN:
+        required: false
+      APPSEC_BOT_SLACK_WEBHOOK:
+        required: false
+  workflow_dispatch:
+
+jobs:
+  run-security-scan:
+    name: Run security scan
+    runs-on: ubuntu-latest
+    permissions:
+      actions: read
+      contents: read
+      security-events: write
+    steps:
+      - name: Analyze code
+        uses: MetaMask/action-security-code-scanner@v1
+        with:
+          repo: ${{ github.repository }}
+          paths_ignored: |
+            '**/*.test.js*'
+            '**/*.test.ts*'
+            '**/docs/'
+            '**/playwright.config.ts'
+            '**/test/'
+            '**/vitest.config*.ts'
+            node_modules
+          project_metrics_token: ${{ secrets.SECURITY_SCAN_METRICS_TOKEN }}
+          slack_webhook: ${{ secrets.APPSEC_BOT_SLACK_WEBHOOK }}