feat: implement systemd service fails after reboot lab for Issue #37

[HimanM]

Description

This PR implements the systemd-broken beginner-level Linux troubleshooting lab, which simulates a scenario where a systemd service fails to start after reboot due to an incorrect ExecStart path in the unit file (Issue #37).

Additionally, this PR updates the backend engine and local test script to dynamically sanitize carriage returns (\r) in user data and shell scripts. This prevents line-ending compatibility issues (such as 203/EXEC or command/file name errors) when tests are run from Windows environments.

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.
• The solution.md provides the step-by-step solution to fix the environment.
• The question.md provides the question for the lab.
• Follows the LAB_FORMAT.md guidelines.
• 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 [LAB IDEA] Systemd Service Fails After Reboot #37