Create semgrep.yml (#28)

### Okta CIC Product Security Assurance - Add semgrep.yml

#### Description
Adds an Semgrep YAML definition file semgrep.yml. This file allows
Semgrep to automatically scan PR changes for vulnerabilities.


#### References

- Official Documentation: [Semgrep
Documentation](https://semgrep.dev/docs/)


#### Testing
No testing is required from you as repository owners.

.github/workflows/semgrep.yml

@@ -0,0 +1,20 @@
+name: Semgrep
+
+on:
+  pull_request_target: {}
+  push:
+    branches: ["master", "main"]
+permissions:
+  contents: read
+jobs:
+  semgrep:
+    name: Scan
+    runs-on: ubuntu-latest
+    container:
+      image: returntocorp/semgrep
+    if: (github.actor != 'dependabot[bot]' && github.actor != 'snyk-bot')
+    steps:
+      - uses: actions/checkout@v3
+      - run: semgrep ci
+        env:
+          SEMGREP_APP_TOKEN: ${{ secrets.SEMGREP_APP_TOKEN }}