feat(execution): Bump LastUpdated on schedule update

[irvinlim]

Closes #50 and #12.

• Separate spec.schedule.constraints.notBefore to spec.schedule.lastUpdated, to avoid conflation of server-managed field vs user-defined fields.
• Add notAfter constraint, the dual of notBefore.
• Fixes JobConfigMutatingWebhook to handle case when cron was not updated but disabled was updated.

[codecov]

Codecov Report

Merging #52 (8d93151) into main (031b4ff) will increase coverage by 0.01%.
The diff coverage is 81.57%.

@@            Coverage Diff             @@
##             main      #52      +/-   ##
==========================================
+ Coverage   54.69%   54.71%   +0.01%     
==========================================
  Files         163      163              
  Lines        8128     8133       +5     
==========================================
+ Hits         4446     4450       +4     
- Misses       3474     3477       +3     
+ Partials      208      206       -2     

Impacted Files	Coverage Δ
apis/execution/v1alpha1/jobconfig_types.go	100.00% <ø> (ø)
...tion/controllers/jobconfigcontroller/reconciler.go	0.00% <0.00%> (ø)
apis/execution/v1alpha1/zz_generated.deepcopy.go	55.22% <40.00%> (-1.39%)	⬇️
...g/execution/controllers/croncontroller/schedule.go	86.58% <100.00%> (+1.25%)	⬆️
pkg/execution/mutation/mutation.go	89.18% <100.00%> (+4.57%)	⬆️

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