Add InputDigest support to CustomTemplateTagger

[mikekamornikov]

Fixes: #5660
Related: #5192

Description
Allows InputDigest to be added to a map of taggers of CustomTemplateTagger.

[mikekamornikov]

@piotr-szybicki I'm not sure if it's enough assuming func (t *customTemplateTagger) EvaluateComponents itself makes additions to customMap in the runtime. But this way it creates the tags I expect.

[codecov]

Codecov Report

Merging #5661 (93d2e81) into master (89b8315) will increase coverage by 0.13%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##           master    #5661      +/-   ##
==========================================
+ Coverage   70.53%   70.66%   +0.13%     
==========================================
  Files         410      410              
  Lines       15639    15672      +33     
==========================================
+ Hits        11031    11075      +44     
+ Misses       3794     3784      -10     
+ Partials      814      813       -1     

Impacted Files	Coverage Δ
pkg/skaffold/tag/tagger_mux.go	68.96% <80.00%> (+2.29%)	⬆️
pkg/skaffold/docker/parse.go	84.32% <0.00%> (-1.09%)	⬇️
pkg/skaffold/runner/dev.go	72.22% <0.00%> (-0.79%)	⬇️
pkg/skaffold/runner/build_deploy.go	68.68% <0.00%> (-0.21%)	⬇️
pkg/skaffold/event/event.go	91.10% <0.00%> (ø)
pkg/skaffold/errors/errors.go	94.54% <0.00%> (+1.81%)	⬆️
pkg/skaffold/runner/deploy.go	51.35% <0.00%> (+2.05%)	⬆️
pkg/skaffold/util/tar.go	56.00% <0.00%> (+5.33%)	⬆️
pkg/skaffold/event/v2/event.go	67.55% <0.00%> (+6.38%)	⬆️
pkg/skaffold/tag/input_digest.go	29.26% <0.00%> (+12.19%)	⬆️

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[MarlonGamez]

lgtm! Confirmed working locally. Thanks for taking the time to add this and update tests as well :) I'll merge once kokoro runs