chore: Use config.furiko.io/v1alpha1 for all Config API types

[irvinlim]

We change the config.furiko.io/v1 API group to config.furiko.io/v1alpha1 first.

The API version of config.furiko.io is NOT the same as the API version of other APIs, e.g. execution.furiko.io. It is simply meant to signify that the configuration format is currently in alpha state.

[codecov]

Codecov Report

Merging #36 (acefa7a) into main (96bb8ca) will not change coverage.
The diff coverage is 40.00%.

@@           Coverage Diff           @@
##             main      #36   +/-   ##
=======================================
  Coverage   49.74%   49.74%           
=======================================
  Files         159      159           
  Lines        7988     7988           
=======================================
  Hits         3974     3974           
  Misses       3831     3831           
  Partials      183      183           

Impacted Files	Coverage Δ
apis/config/v1alpha1/managerconfig_types.go	100.00% <ø> (ø)
apis/config/v1alpha1/webhookconfig_types.go	100.00% <ø> (ø)
apis/config/v1alpha1/zz_generated.deepcopy.go	0.00% <0.00%> (ø)
cmd/execution-controller/main.go	0.00% <0.00%> (ø)
cmd/execution-webhook/main.go	0.00% <0.00%> (ø)
...execution/controllers/croncontroller/controller.go	23.07% <ø> (ø)
pkg/execution/controllers/croncontroller/cron.go	0.00% <0.00%> (ø)
...kg/execution/controllers/croncontroller/factory.go	0.00% <ø> (ø)
...execution/controllers/croncontroller/reconciler.go	87.34% <ø> (ø)
...tion/controllers/jobconfigcontroller/controller.go	0.00% <ø> (ø)
... and 41 more

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