Fix M-112 and use CEL optional values and variables in built-in checks

[matheusfm]

Description

This PR

• Updates most built-in checks to use optional values and variables to improve the readability of CEL expressions;
• Fixes the check M-112 to fail if allowPrivilegeEscalation is not set (references: pod-security-admission unit test and Privilege Escalation check of Pod Security Standards);
• Updates the checks M-112 (privilege escalation), M-115 (seccomp), and M-116 (capabilities) to be skipped for pods in windows nodes, as recommended by Kubernetes documentation.

Note that all built-in checks have unit tests with different cases.

Linked Issues

UD-1283

How has this been tested?

• Running unit tests: make test
• Scanning a cluster: go run main.go scan

Checklist

• I have labeled this PR with the relevant Type labels
• I have documented my code (if applicable)
• My changes are covered by tests