Rename Store resource to ClusterStore

[tylerphelan]

• Kept StoreReader, StoreBuildpack, and StoreImage types
• Some import changes

[codecov-commenter]

Codecov Report

Merging #434 into master will increase coverage by 0.07%.
The diff coverage is 68.33%.

@@            Coverage Diff             @@
##           master     #434      +/-   ##
==========================================
+ Coverage   67.33%   67.40%   +0.07%     
==========================================
  Files          85       85              
  Lines        3612     3620       +8     
==========================================
+ Hits         2432     2440       +8     
  Misses        894      894              
  Partials      286      286              

Impacted Files	Coverage Δ
pkg/apis/build/v1alpha1/builder_types.go	0.00% <ø> (ø)
pkg/apis/build/v1alpha1/cluster_builder.go	0.00% <ø> (ø)
.../apis/experimental/v1alpha1/cluster_store_types.go	0.00% <0.00%> (ø)
...apis/experimental/v1alpha1/custom_builder_types.go	0.00% <ø> (ø)
pkg/apis/experimental/v1alpha1/register.go	0.00% <0.00%> (ø)
pkg/cnb/buildpack_validation.go	100.00% <ø> (ø)
pkg/reconciler/sourceresolver/enqueuer.go	100.00% <ø> (ø)
pkg/secret/fetcher.go	0.00% <0.00%> (ø)
pkg/reconciler/custombuilder/custombuilder.go	46.15% <60.00%> (ø)
...ciler/customclusterbuilder/customclusterbuilder.go	46.15% <60.00%> (ø)
... and 5 more

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[tylerphelan]

execute_build_test.go fixed in #437

[tylerphelan]

closing this in favor of #437 where both renames will occur