Fix array node serialize with corresponding plugin custom.

[chaohengstudent]

Tracking issue

Closes flyteorg/flyte#4515

Why are the changes needed?

Have to get the corresponding custom to operate plugins with array node map task.

What changes were proposed in this pull request?

Inherit func get_custom() with python_function_task in array_node_map_task.py

How was this patch tested?

Testing kftensorflow with array node in sandbox.

Screenshots

Check all the applicable boxes

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

Related PRs

Docs link

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (a34ab93) 86.14% compared to head (fe47974) 54.61%.

Files	Patch %	Lines
flytekit/core/array_node_map_task.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #2014       +/-   ##
===========================================
- Coverage   86.14%   54.61%   -31.54%     
===========================================
  Files         320      173      -147     
  Lines       23441    16770     -6671     
  Branches     3458     3458               
===========================================
- Hits        20194     9159    -11035     
- Misses       2655     7201     +4546     
+ Partials      592      410      -182     

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