Request to make steps draggable and sortable while editing Pipeline graphically

[JohnNiang]

trafficstars

What would you like to be added:

Request to make steps draggable and sortable while editing Pipeline graphically.

Or we could put Add step and Add nesting step button before and after one step. Just like this:

  ,----------.  
  |+ Add step|  
  |----------|  
  `----------'  
        |       
        |       
,--------------.
|This is a step|
|--------------|
|              |
|              |
|              |
|              |
|              |
`--------------'
        |       
  ,----------.  
  |+ Add step|  
  |----------|  
  `----------'  

Why is this needed:

It's painful that we need to insert a step at the beginning of a stage. We have to remember current steps, delete them, insert new step at the beginning and re-insert others deleted just now.

/kind feature /area devops

/cc @kubesphere/sig-console /cc @kubesphere/sig-devops

[LinuxSuRen]

/area console