refactor(helper): merge single and single_multi_input into one

[hanxiao]

No description provided.

[Yongxuanzhang]

Maybe need to merge/rebase master to pass docstring and black CI?

[github-actions]

Latency summary

Current PR yields:

• 😶 index QPS at 937, delta to last 3 avg.: +0%
• 😶 query QPS at 13, delta to last 3 avg.: -5%

Breakdown

Version	Index QPS	Query QPS
current	937	13
1.0.10	944	13
1.0.9	934	13

Backed by latency-tracking. Further commits will update this comment.

[nan-wang]

The executors in jina-hub need to be adapted as well.

https://github.com/jina-ai/jina-hub/search?q=single_multi_input

[codecov]

Codecov Report

Merging #2192 (14fc323) into master (b5f8010) will decrease coverage by 2.70%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2192      +/-   ##
==========================================
- Coverage   90.50%   87.80%   -2.71%     
==========================================
  Files         208      208              
  Lines       11243    11222      -21     
==========================================
- Hits        10175     9853     -322     
- Misses       1068     1369     +301     

Flag	Coverage Δ
daemon	50.24% <9.09%> (+0.04%)	⬆️
jina	88.12% <100.00%> (-2.84%)	⬇️

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

Impacted Files	Coverage Δ
jina/drivers/segment.py	78.12% <ø> (+2.36%)	⬆️
jina/executors/decorators.py	94.24% <100.00%> (-0.08%)	⬇️
jina/schemas/pod.py	0.00% <0.00%> (-100.00%)	⬇️
jina/schemas/flow.py	0.00% <0.00%> (-100.00%)	⬇️
jina/schemas/meta.py	0.00% <0.00%> (-100.00%)	⬇️
jina/schemas/driver.py	0.00% <0.00%> (-100.00%)	⬇️
jina/schemas/request.py	0.00% <0.00%> (-100.00%)	⬇️
jina/schemas/executor.py	0.00% <0.00%> (-100.00%)	⬇️
jina/schemas/__init__.py	7.14% <0.00%> (-92.86%)	⬇️
jina/parsers/export_api.py	0.00% <0.00%> (-87.50%)	⬇️
... and 19 more

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[JoanFM]

Documentation needs update