Support cluster new/init

[BusyJay]

Feature Request

Describe the feature you'd like:
I would like a command "new" or "init" to help build up a cluster configuration. It's very inconvenient to write topology.yaml now. I have to search and then copy/paste and do customization.

With the new command, user doesn't need to search around anymore. A new command should create a folder and then create an example topology.yaml inside the folder. An init command should just create an the file in current directory.

new can also accept a template name to indicate what the deploy topology is. So users just need to update the details like hosts and ports without remembering the boilerplate.

[lonng]

@BusyJay This feature in our roadmap. And we will implement it in Apri.

[AstroProfundis]

The tiup-cluster template subcommand is supported in v1.4.0.