gitleaks is not installed by GDK setup on Linux, and the pre-commit hook passes even when it's not installed

Overview

On Linux, gitleaks is not installed by the GDK setup because brew isn't available. When running git commit a warning is shown for "gitleaks is not installed", but in the summary section, secrets-detection is marked with a green checkbox, and the pre-commit hook passes:

This is easy to miss and can (and did) cause someone to accidentally commit and push up an API key, and the pre-commit hook does not stop it from happening. We should do 2 things:

1. If possible, modify the GDK setup so that it installs gitleaks on Linux.
2. Fail the pre-commit hook if gitleaks is not installed.

Impacted categories

The following categories relate to this issue:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Steps to replicate (optional)

Proposal (optional)

Environment (optional)

• Operating system name: Linux Ubuntu 5.19.0-41-generic #42~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Tue Apr 18 17:40:00 UTC 2 x86_64 x86_64 x86_64 GNU/Linux
• Architecture: x86_64
• The contents of your gdk.yml (if any)
• Ruby version: ruby 3.0.5p211 (2022-11-24 revision ba5cf0f7c5) [x86_64-linux]
• GDK version: 432eb4f1