[Feat] add sleep plugin

[machichima]

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Why are the changes needed?

What changes were proposed in this pull request?

How was this patch tested?

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• added: For new features.
• changed: For changes in existing functionality.
• deprecated: For soon-to-be-removed features.
• removed: For features being removed.
• fixed: For any bug fixed.
• security: In case of vulnerabilities

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• I updated the documentation accordingly.
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[codecov]

Codecov Report

❌ Patch coverage is 62.02532% with 30 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.22%. Comparing base (51877f8) to head (5e1840b).

Files with missing lines	Patch %	Lines
flyteplugins/go/tasks/plugins/core/sleep/plugin.go	62.02%	20 Missing and 10 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7579   +/-   ##
=======================================
  Coverage   57.22%   57.22%           
=======================================
  Files         930      931    +1     
  Lines       58190    58269   +79     
=======================================
+ Hits        33297    33346   +49     
- Misses      21840    21860   +20     
- Partials     3053     3063   +10     

Flag	Coverage Δ
unittests-datacatalog	53.51% <ø> (ø)
unittests-flyteadmin	53.23% <ø> (ø)
unittests-flytecopilot	48.05% <ø> (ø)
unittests-flytectl	64.09% <ø> (ø)
unittests-flyteidl	75.71% <ø> (ø)
unittests-flyteplugins	60.39% <62.02%> (+0.01%)	⬆️
unittests-flytepropeller	53.78% <ø> (ø)
unittests-flytestdlib	64.39% <ø> (ø)

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