Add SAST security checks with SECURITY.md #178

This commit incorporates Static Analysis Security Testing (SAST) using
CodeQL. This integration will enforce consistent security assessments
with every change and on a predetermined schedule.

This commit also involves a restructure of security checks. The existing
security-checks workflow is renamed to better reflect its functionality
related to dependency audits.

These changes will enhance the project's resilience against potential
vulnerabilities in both the codebase and third-party dependencies.

Changes include:

- Remove older LGTM badge that's replaced by SAST checks.
- Rename `checks.security.yaml` to `checks.security.dependencies.yaml`,
  reinforcing the focus on dependency audits.
- Update `README.md`, ensuring the clear representation of security
  check statuses, including new SAST integration.
- Add new `SECURITY.md`, establishing the protocol for reporting
  vulnerabilities and outlining the project's commitment to robust
  security testing.
- Enhance `docs/tests.md` with detailed information on the newly
  integrated security checks.
- Add reference to SECURITY.md in README.md.

.github/workflows/checks.security.sast.yaml

@@ -0,0 +1,42 @@
+name: checks.security.sast
+
+on:
+  push:
+  pull_request:
+  schedule:
+    - cron: '0 0 * * 0' # at 00:00 on every Sunday
+
+jobs:
+  analyze:
+    name: Analyze
+    runs-on: ubuntu-latest
+    permissions:
+      actions: read
+      contents: read
+      security-events: write
+
+    strategy:
+      fail-fast: false
+      matrix:
+        language: [
+          javascript # analyzes code written in JavaScript, TypeScript and both.
+        ]
+
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v3
+      -
+        name: Initialize CodeQL
+        uses: github/codeql-action/init@v2
+        with:
+          languages: ${{ matrix.language }}
+          queries: +security-and-quality
+      -
+        name: Autobuild
+        uses: github/codeql-action/autobuild@v2
+      -
+        name: Perform CodeQL Analysis
+        uses: github/codeql-action/analyze@v2
+        with:
+          category: "/language:${{ matrix.language }}"