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.

SECURITY.md

@@ -0,0 +1,31 @@
+# Security Policy
+
+privacy.sexy takes security seriously. Commitment is made to address all security issues with urgency. Responsible reporting of any discovered vulnerabilities in the project is highly encouraged.
+
+## Reporting a Vulnerability
+
+Efforts to responsibly disclose findings are greatly appreciated. To report a security vulnerability, follow these steps:
+
+- For general vulnerabilities, [open an issue](https://github.com/undergroundwires/privacy.sexy/issues/new/choose) using the bug report template.
+- For sensitive matters, [contact the developer directly](https://undergroundwires.dev).
+
+## Security Report Handling
+
+Upon receipt of a security report, the following actions will be taken:
+
+- The report will be confirmed, identifying the affected components.
+- The impact and severity of the issue will be assessed.
+- Work on a fix and plan a release to address the vulnerability will be initiated.
+- The reporter will be kept updated about the progress.
+
+## Testing
+
+Regular and extensive testing is conducted to ensure robust security in the project. Information about testing practices can be found in the [Testing Documentation](./docs/tests.md).
+
+## Support
+
+For additional assistance or any unanswered questions, [submit a GitHub issue](https://github.com/undergroundwires/privacy.sexy/issues/new/choose). Security concerns are a priority, and necessary support to address them is assured.
+
+---
+
+Active contribution to the safety and security of privacy.sexy is thanked. This collaborative effort keeps the project resilient and trustworthy for all.