Implement Ap

[yitsushi]

Only one endpoint: ap/show

Documentation: https://misskey.io/api-doc#operation/ap/show

[yitsushi]

[discussion moved from #4]

I added some response JSON files as a fixture: https://github.com/yitsushi/go-misskey/tree/main/services/federation/fixtures/ap-show

Move them into the right place.

[discussion]
Maybe ap/show should live in its own service "client.Ap()" and all possible types will be added as a new function like client.Ap().ShowNote(string uri). It should have only one ShowRequest and a Show() function that returns with an ShowResponse and all other functions would just call that Show() function and typecast the Object property and return only with that property.

type ShowResponse struct {
  Type string `json:"type"`
  Object interface{} `json:"object"`
}

That way if someone wants to query an unimplemented resource or they want to use it as a detector "I got this URI, what is its type?", they can use Show() and use the type field to check what its Type, but if they know the resource type or they want a specific resource type like Note if it's not a Node they want an error, they can use the ShowNote() function.