Design the `client` package API

[noahingh]

I will collect APIs under the api pkg to let users reference them when interacting with the server. I'll design the package to let users can easily reference it.

Example

func main() {
	ctx := context.Background()
	ts := oauth2.StaticTokenSource(
		&oauth2.Token{AccessToken: "... your access token ..."},
	)
        tc := oauth2.NewClient(ctx, ts)
        
        c := api.NewClient(...)
        ds, _ := c.Search.ListDeployments(ctx, ...)
}