chore(ci): add gitleaks scan

[nevermarine]

Description

Add gitleaks diff scan for PRs and full scan for schedule or for manual workflow run.

Why do we need it, and what problem does it solve?

What is the expected result?

Checklist

• The code is covered by unit tests.
• e2e tests passed.
• Documentation updated according to the changes.
• Changes were tested in the Kubernetes cluster manually.

Changelog entries

section: ci
type: chore
summary: add gitleaks scan