Add CodeQL code scanning and extend Dependabot coverage (#29)

[szachovy]

Summary

Adds code scanning with CodeQL and extends Dependabot coverage to address #29.

Changes

CodeQL Code Scanning (.github/workflows/codeql.yml)

• Runs Python static analysis on every push and weekly (Monday 06:00 UTC)
• Reports findings to the GitHub Security tab under Code scanning alerts
• Uses github/codeql-action/init@v3 and github/codeql-action/analyze@v3

Dependabot Updates (.github/dependabot.yml)

• Added github-actions ecosystem to keep CI/CD action versions up to date
• Added terraform ecosystem to keep Terraform provider versions up to date
• Existing docker and pip ecosystems remain unchanged

Documentation

• Added Supply Chain Security section to docs/SECURITY.md covering code scanning and dependency management
• Updated CHANGELOG.md with new entries

Closes #29

[github-advanced-security]

You are seeing this message because GitHub Code Scanning has recently been set up for this repository, or this pull request contains the workflow file for the Code Scanning tool.

What Enabling Code Scanning Means:

• The 'Security' tab will display more code scanning analysis results (e.g., for the default branch).
• Depending on your configuration and choice of analysis tool, future pull requests will be annotated with code scanning analysis results.
• You will be able to see the analysis results for the pull request's branch on this overview once the scans have completed and the checks have passed.

For more information about GitHub Code Scanning, check out the documentation.