Provide example of custom Conduit with the CLI included

[hariso]

Feature description

Currently, our example/recommendation to implement a custom Conduit instance (e.g. with built-in connectors) is this:

package main

import (
	http "github.com/conduitio-labs/conduit-connector-http"
	"github.com/conduitio/conduit/pkg/conduit"
)

func main() {
	// Get the default configuration, including all built-in connectors
	cfg := conduit.DefaultConfig()

	// Add the HTTP connector to list of built-in connectors
	cfg.ConnectorPlugins["http"] = http.Connector

	conduit.Serve(cfg)
}

(Taken from https://conduit.io/docs/using/connectors/additional-built-in-plugins/)

However, with the introduction of CLI, the example above won't include the CLI.

The goal of this issue is to provide a way to build a custom Conduit with the CLI included.