use docker/reference.Store to manage tags/digest by app image ID

[ndeloof]

- What I did Used docker/reference to implement imageStore

- How I did it only store images by ID, use docker/reference to track tags/digest

- How to verify it e2e test suite cover most usages

- Description for the changelog re-implemented bundle store

- A picture of a cute animal (not mandatory)

[codecov[bot]]

Codecov Report

Merging #782 into master will decrease coverage by 0.3%. The diff coverage is 71.81%.

@@            Coverage Diff             @@
##           master     #782      +/-   ##
==========================================
- Coverage   70.43%   70.13%   -0.31%     
==========================================
  Files          67       67              
  Lines        3734     3676      -58     
==========================================
- Hits         2630     2578      -52     
+ Misses        756      753       -3     
+ Partials      348      345       -3

Impacted Files	Coverage Δ
internal/cnab/cnab.go	32.3% <0%> (ø)	:arrow_up:
internal/store/digest.go	85.18% <100%> (+1.18%)	:arrow_up:
internal/packager/bundle.go	64% <100%> (ø)	:arrow_up:
internal/commands/image/tag.go	84.21% <100%> (ø)	:arrow_up:
internal/commands/push.go	34.07% <66.66%> (-0.02%)	:arrow_down:
internal/store/image.go	72.32% <70.21%> (-4.25%)	:arrow_down:

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[aiordache]

LGTM