feat: Add CronController tests

[irvinlim]

Pending #27 to be merged, since we are using some dependencies from that branch.

This PR adds further tests for CronController, and also refactors some of the scaffold to be more suitable for dependency injection.

[codecov]

Codecov Report

Merging #30 (b3ec3c5) into main (31d88de) will increase coverage by 1.79%.
The diff coverage is 64.21%.

@@            Coverage Diff             @@
##             main      #30      +/-   ##
==========================================
+ Coverage   47.26%   49.05%   +1.79%     
==========================================
  Files         158      160       +2     
  Lines        7934     7952      +18     
==========================================
+ Hits         3750     3901     +151     
+ Misses       3994     3864     -130     
+ Partials      190      187       -3     

Impacted Files	Coverage Δ
cmd/execution-controller/main.go	0.00% <0.00%> (ø)
...lers/jobqueuecontroller/reconciler_perjobconfig.go	0.00% <0.00%> (ø)
pkg/runtime/controllercontext/context_stores.go	16.66% <ø> (ø)
...execution/controllers/croncontroller/controller.go	23.07% <5.00%> (+23.07%)	⬆️
pkg/utils/testutils/uid.go	55.55% <55.55%> (ø)
...kg/execution/controllers/croncontroller/control.go	100.00% <100.00%> (ø)
...execution/controllers/croncontroller/reconciler.go	87.34% <100.00%> (+87.34%)	⬆️
pkg/execution/controllers/croncontroller/util.go	81.81% <100.00%> (+1.17%)	⬆️
pkg/execution/stores/activejobstore/store.go	70.21% <100.00%> (+4.21%)	⬆️
...ersioned/typed/execution/v1alpha1/fake/fake_job.go	73.23% <0.00%> (+8.45%)	⬆️
... and 4 more

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