[doc] Add examples of piped config for each platform

[t-kikuc]

What would you like to be added:

We need examples of piped config files, which are related to https://pipecd.dev/docs/user-guide/managing-piped/adding-a-platform-provider/.
Especially, there are two ways for Kubernetes: to the same cluster and to an external cluster.

Why is this needed:

To inform users clearly how to configure piped.

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[t-kikuc]

we'll do it with pipedv1 because pipedv1 will change piped-config.

[t-kikuc]

I mean we will not create for pipedv0.