`dobi list` grouped by tags

[siredmar]

It would be nice if dobi hat a way not only to list all resources and possible tags, but show a kind of grouped list dependend on the tags.

Currently all resources are listed unsorted. There is a way to make the list view more specific with the tags option.
I propose an option called -g,--groups, that makes the output a little bit more structured.

Example original:

$ dobi list
Resources:
  job0
  job1
  job2
  image1
  job1
  job3
  image2

Tags: 
  dev, prod

Example with -g:

$ dobi list -g
Resources:
  job0
  Tag: dev
    job1
    job2
    image1
  Tag: prod
    job1
    job3
    image2
Tags: 
  dev, prod