docs: Add example for security agent readiness

[ajaysundark]

A use-case commonly seen in kubernetes cluster is to ensure a security-agent (eg Falco is installed on the node to ensure security controls are active before allowing workloads on the node.

We could document this as an example, following the pattern of the CNI Readiness example

• Create a new documentation page at docs/book/src/examples/security-agent-readiness.md.
• Include a sample NodeReadinessRule configuration for the security agent installation.
• Briefly explain the problem (workloads starting before security monitoring) and the solution.
• Update docs/book/src/SUMMARY.md to include the new page.

[ajaysundark]

cc @arnab-logs

[arnab-logs]

/assign