feat(execution): Implement parallelism in Job

[irvinlim]

Closes #71.

This implements all necessary features to support parallel tasks in a single Job. The following changes are introduced:

1. Added API changes to introduce ParallelismSpec according to the proposal in Proposal: Support task-level parallelism #71.
2. Revamped API for JobStatus fields, and reduced the possible set of phase, results, states, etc. to reduce duplication.
3. Changed the job and task naming convention to delimit name components with hyphens instead of periods (e.g. jobconfig-parallel-1653824280 and jobconfig-parallel-sleep-1653822660-ge3tgm-0)
4. Added mutation and validation handlers for ParallelismSpec.
5. Compute uncreated tasks and create them in reconciler.

Remaining TODO items:

• Immediately terminate all remaining tasks when a single task fails (all retries exceeded) when using AllSuccessful
• Create reconciler integration tests

[codecov]

Codecov Report

Merging #81 (1343c81) into main (fe5f311) will increase coverage by 0.18%.
The diff coverage is 75.96%.

@@            Coverage Diff             @@
##             main      #81      +/-   ##
==========================================
+ Coverage   62.60%   62.79%   +0.18%     
==========================================
  Files         197      199       +2     
  Lines        9858    10340     +482     
==========================================
+ Hits         6172     6493     +321     
- Misses       3373     3499     +126     
- Partials      313      348      +35     

Impacted Files	Coverage Δ
...g/execution/taskexecutor/podtaskexecutor/labels.go	100.00% <ø> (ø)
pkg/execution/util/job/job_utils.go	60.00% <ø> (-24.38%)	⬇️
pkg/execution/mutation/mutation.go	83.74% <27.27%> (-4.34%)	⬇️
pkg/utils/time/time.go	48.00% <46.66%> (-2.00%)	⬇️
...ecution/taskexecutor/podtaskexecutor/pod_lister.go	80.64% <50.00%> (-8.25%)	⬇️
pkg/execution/util/job/task.go	50.00% <50.00%> (ø)
pkg/execution/variablecontext/provider.go	58.69% <53.84%> (+5.75%)	⬆️
...ecution/taskexecutor/podtaskexecutor/pod_client.go	78.57% <57.14%> (+1.64%)	⬆️
.../execution/controllers/jobcontroller/reconciler.go	70.92% <57.66%> (-4.08%)	⬇️
apis/execution/v1alpha1/zz_generated.deepcopy.go	60.40% <67.03%> (-0.62%)	⬇️
... and 26 more

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