Add nodeName template var and update doc

[ketian-indeed]

Tracking issue

Closes #6086

Why are the changes needed?

See #6086 for more details.

What changes were proposed in this pull request?

1. added a new template variable {{ .nodeName }} that will return the pod's spec.nodeName;
2. also updated the doc accordingly.

How was this patch tested?

Unit tests added.

Check all the applicable boxes

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

Related PRs

#4939

Docs link

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[ketian-indeed]

A friendly bump @ppiegaze @eapolinario 🙇

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 37.01%. Comparing base (7aeaa26) to head (e83ad6f).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6088   +/-   ##
=======================================
  Coverage   37.00%   37.01%           
=======================================
  Files        1318     1318           
  Lines      132516   132519    +3     
=======================================
+ Hits        49037    49046    +9     
+ Misses      79235    79229    -6     
  Partials     4244     4244           

Flag	Coverage Δ
unittests-datacatalog	51.58% <ø> (ø)
unittests-flyteadmin	54.23% <ø> (+0.02%)	⬆️
unittests-flytecopilot	30.99% <ø> (ø)
unittests-flytectl	62.29% <ø> (ø)
unittests-flyteidl	7.23% <ø> (ø)
unittests-flyteplugins	53.86% <100.00%> (+<0.01%)	⬆️
unittests-flytepropeller	42.59% <ø> (ø)
unittests-flytestdlib	55.18% <ø> (ø)

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