enhancement(4889): added check to abort enrolling if user is privileg…

[kaanyalti]

• Enhancement

What does this PR do?

This PR updates the enroll command so that it provides a more descriptive error message to the user in the case a root user tries to enroll an unprivileged agent.

Why is it important?

Provides users with clearer information.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool
• I have added an integration test or an E2E test

How to test this PR locally

• Create an agent policy, install and enroll and agent in unprivileged mode
• Unenroll the agent
• Try to enroll the agent with root user, validate the error message

Related issues

• Closes Actionable error message when attempting to enroll an unprivileged Agent as a privileged user #4889

[mergify]

This pull request does not have a backport label. Could you fix it @kaanyalti? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-./d./d is the label to automatically backport to the 8./d branch. /d is the digit

[mergify]

backport-v8.x has been added to help with the transition to the new branch 8.x.
If you don't need it please use backport-skip label and remove the backport-8.x label.

[elastic-sonarqube]

Quality Gate passed

Issues
2 New issues
1 Fixed issue
0 Accepted issues

Measures
0 Security Hotspots
45.5% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube