Improve docs for CNI with Cilium

[lukidzi]

Description

When users deploy Kong Mesh with CNI and Cilium, the configuration steps may vary depending on how Cilium was installed. The paths differ based on whether:

• Cilium is provided by a cloud provider,
• Cilium is installed manually by the user, or
• Cilium is not used in a public cloud environment.

This can create confusion, so we should provide clear, explicit instructions that cover each installation scenario. This way, users will know which configurations to apply based on their Cilium setup, ensuring a smoother setup experience with Kong Mesh.