[WIP] Add --digests flag to image ls command to show app image digests

[jcsirot]

- What I did Add --digests flag to docker app image ls command

- How to verify it the docker app image ls --digests should output a similar message in the console

$ docker app image ls --digests
REPOSITORY        TAG   DIGEST                                                                  APP NAME
my-app            1.0.1 <none>                                                                  voting-app
rumpl/hello-world 1.0.0 sha256:2d2417f6bdedb3cf701f91565fec682bfb60032b51fa4e955b918e4ac4cc618d hello-world

- A picture of a cute animal (not mandatory but encouraged)

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@90d8144). Click here to learn what that means. The diff coverage is 47.05%.

@@            Coverage Diff            @@
##             master     #677   +/-   ##
=========================================
  Coverage          ?   70.91%           
=========================================
  Files             ?       56           
  Lines             ?     2912           
  Branches          ?        0           
=========================================
  Hits              ?     2065           
  Misses            ?      582           
  Partials          ?      265

Impacted Files	Coverage Δ
internal/commands/image/list.go	64.55% <47.05%> (ø)

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[jcsirot]

superseded by #709