Add support for workflow - fan-out/fan-in pattern

[mikeee]

Description

Adds an interface to create a slice of tasks that can be executed in parallel.

Validation example created -workflow-parallel and added to the validation run.

Issue reference

Please reference the issue this PR will close: #508

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• [x] Code compiles correctly
• [x] Created/updated tests
• [x] Extended the documentation

[codecov[bot]]

Codecov Report

Attention: 372 lines in your changes are missing coverage. Please review.

Comparison is base (cefbadb) 70.11% compared to head (59d35de) 58.04%. Report is 4 commits behind head on main.

Files	Patch %	Lines
examples/workflow/main.go	0.00%	182 Missing :warning:
examples/workflow-parallel/main.go	0.00%	78 Missing :warning:
workflow/client.go	50.61%	38 Missing and 2 partials :warning:
workflow/worker.go	55.38%	25 Missing and 4 partials :warning:
workflow/workflow.go	56.86%	21 Missing and 1 partial :warning:
workflow/context.go	50.00%	17 Missing :warning:
client/client.go	0.00%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #509 +/- ## =========================================== - Coverage 70.11% 58.04% -12.07% =========================================== Files 35 55 +20 Lines 2884 3568 +684 =========================================== + Hits 2022 2071 +49 - Misses 748 1375 +627 - Partials 114 122 +8 ```

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[mikeee]

@yaron2 - minor non-breaking addition to workflows that should be included in the release.