text: Title: Improve pipeline plot
  Body: The output plot is pretty boring:
  
  ![index](https://user-images.githubusercontent.com/989250/138205596-bc314e8d-eecb-4137-b922-41b954db5bbf.png)
  
  We're using pygraphviz to generate it and it has lots of customization options to make it better.
  
  Here's the code that generates the plot:
  
  https://github.com/ploomber/ploomber/blob/068df147c2c9af0f998beb6128e13fffe16e86e3/src/ploomber/dag/dag.py#L787
  
  https://github.com/ploomber/ploomber/blob/f6013f9b21ae644976c1696b1d989968d1042602/src/ploomber/dag/dag.py#L820
  
  The fix involves checking the options we have in https://graphviz.org/ to make the plot prettier
  
  To get started, you can clone one example and generate one plot: https://docs.ploomber.io/en/latest/user-guide/templates.html
  
  one option we should have is to only show task names (hide products)
  
  
  
  - [x] option to hide products
  - [x] document option to hide products in the .rst docs
  - [x] improve the plot style (colors, font size, etc)
  