fix: use docker lib for image ref parsing

[catthehacker]

Fixes #795

The only downside is custom URL can't be, e.g.: localhost:8000/_/ubuntu:latest

Signed-off-by: hackercat me@hackerc.at

[codecov]

Codecov Report

Merging #877 (faa964c) into master (0f04942) will increase coverage by 6.89%.
The diff coverage is 60.95%.

@@            Coverage Diff             @@
##           master     #877      +/-   ##
==========================================
+ Coverage   49.27%   56.16%   +6.89%     
==========================================
  Files          23       25       +2     
  Lines        2401     3947    +1546     
==========================================
+ Hits         1183     2217    +1034     
- Misses       1090     1528     +438     
- Partials      128      202      +74     

Impacted Files	Coverage Δ
pkg/common/outbound_ip.go	0.00% <0.00%> (ø)
pkg/container/docker_volume.go	0.00% <0.00%> (ø)
pkg/container/docker_run.go	5.56% <15.09%> (+3.63%)	⬆️
pkg/common/git.go	49.82% <31.81%> (-9.97%)	⬇️
pkg/model/planner.go	49.78% <42.50%> (+16.70%)	⬆️
pkg/container/docker_build.go	58.97% <50.00%> (+58.97%)	⬆️
pkg/container/docker_pull.go	28.35% <58.06%> (+10.17%)	⬆️
pkg/model/workflow.go	52.14% <63.63%> (+26.42%)	⬆️
pkg/artifacts/server.go	67.32% <67.32%> (ø)
pkg/runner/runner.go	74.46% <70.37%> (-2.01%)	⬇️
... and 30 more

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