[DOC] add copy command examples and description

[mao3267]

Related PRs

flyteorg/flytekit#2715

Why are the changes needed?

Update the documents for users to understand the copy commands behaviors and usages.

What changes were proposed in this pull request?

1. Added a simple workflow example of using imageSpec with copy commands.
2. Describe the expected behavior and usages.

How was this patch tested?

1. The examples are tested through remote execution.

pyflyte run --remote build_image.py my_wf

Screenshots

Check all the applicable boxes

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

Docs link

TODO

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 36.31%. Comparing base (c0cb4d1) to head (542aae7).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5782      +/-   ##
==========================================
- Coverage   36.31%   36.31%   -0.01%     
==========================================
  Files        1304     1304              
  Lines      110016   110016              
==========================================
- Hits        39950    39948       -2     
- Misses      65909    65911       +2     
  Partials     4157     4157              

Flag	Coverage Δ
unittests-datacatalog	51.37% <ø> (ø)
unittests-flyteadmin	55.62% <ø> (ø)
unittests-flytecopilot	12.17% <ø> (ø)
unittests-flytectl	62.21% <ø> (-0.05%)	⬇️
unittests-flyteidl	7.12% <ø> (ø)
unittests-flyteplugins	53.35% <ø> (ø)
unittests-flytepropeller	41.89% <ø> (ø)
unittests-flytestdlib	55.37% <ø> (+0.02%)	⬆️

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