fix: raise exceptions in path importer

[jemmyshin]

Goals:
Currently, we add all paths into not_python_module_paths but sometimes the exception comes from ImportError(or other types of error). So we need to raise this exception to make the error message clear.

• resolves clip-as-service issue #865

• check and update documentation. See guide and ask the team.

[codecov]

Codecov Report

Merging #5447 (4dcffab) into master (0db2d18) will increase coverage by 0.01%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master    #5447      +/-   ##
==========================================
+ Coverage   87.31%   87.33%   +0.01%     
==========================================
  Files         101      101              
  Lines        6613     6615       +2     
==========================================
+ Hits         5774     5777       +3     
+ Misses        839      838       -1     

Flag	Coverage Δ
jina	87.33% <33.33%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
jina/importer.py	87.20% <33.33%> (-2.08%)	⬇️
jina/serve/runtimes/gateway/request_handling.py	98.13% <0.00%> (+2.80%)	⬆️

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[numb3r3]

LGTM

[samsja]

lgtm