feat: implement cron job never executes lab for Issue #38

[HimanM]

Description

This PR implements the cron-broken lab, which simulates a scheduled cleanup cron job failing to run due to a wrong interpreter (invalid shebang) and incorrect permissions (non-executable script) on the target script /opt/cleanup.sh.

Type of change

• Bug fix
• New feature
• New Lab

Lab Requirements (If submitting a new lab)

If you are submitting a new BrokenOps lab, please verify:

• The lab.yaml is fully populated.
• The cloud-init.yaml correctly breaks the environment.
• The verify.sh script correctly asserts if the environment is fixed.
• MANDATORY: A working solution.sh script is provided to automatically fix the environment. (This is required for our CI verification pipeline).

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas

Closes Issues

• closes issue [LAB IDEA] Cron Job Never Executes #38