Setting up codescanning action

[ganeshkumarsv]

What does this PR do?

Static code analysis on datadog-lambda-rb using Github's Code Scanning.

This PR has Github workflow configs to trigger the Code Scanning on every PR and on push to main branch. As of now only default security based CodeQL queries are configured. We can gradually add queries for Code Quality later. As the repository is small, no security alerts were found during the scan.

Motivation

It is a part of Datadog compliance requirements to regularly perform code-scanning on all the customer installed code.

Testing Guidelines

Additional Notes

Types of changes

• [ ] Bug fix
• [ ] New feature
• [ ] Breaking change
• [ ] Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• [ ] This PR's description is comprehensive
• [ ] This PR contains breaking changes that are documented in the description
• [ ] This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• [ ] This PR impacts documentation, and it has been updated (or a ticket has been logged)
• [ ] This PR's changes are covered by the automated tests
• [ ] This PR collects user input/sensitive content into Datadog