[refactor] move phase constants from pkg/skaffold/errors to pkg/skaffold/constants

[MarlonGamez]

Description
This refactor moves the phase constants from pkg/skaffold/errors to pkg/skaffold/constants. @gsquared94 brought that referencing this values as errors.* was awkward and confusing, so we thought we should move them.

[codecov]

Codecov Report

Merging #5641 (597b657) into master (fd96d77) will decrease coverage by 0.01%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##           master    #5641      +/-   ##
==========================================
- Coverage   70.68%   70.67%   -0.02%     
==========================================
  Files         408      408              
  Lines       15581    15582       +1     
==========================================
- Hits        11014    11013       -1     
- Misses       3757     3758       +1     
- Partials      810      811       +1     

Impacted Files	Coverage Δ
pkg/skaffold/errors/errors.go	92.72% <ø> (ø)
pkg/skaffold/server/v2/endpoints.go	43.24% <0.00%> (ø)
pkg/skaffold/runner/dev.go	72.83% <88.88%> (+0.16%)	⬆️
pkg/skaffold/event/event.go	91.10% <90.00%> (ø)
pkg/skaffold/event/v2/event.go	61.17% <100.00%> (ø)
pkg/skaffold/util/tar.go	50.66% <0.00%> (-5.34%)	⬇️
pkg/skaffold/docker/parse.go	85.40% <0.00%> (+1.08%)	⬆️

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