refactor: optional disable uses_b/a if parallel is 1

[JoanFM]

Changes introduced
Right now if we use uses_before or uses_after it is added even when parallel is 1. Although it can be desired to have a uses_after or uses_before it is more common to only want it when there are multiple Peas inside a Pod.

Add an option to disable them if parallel is 1. Like this one can keep the same Flow structure for sharding and no sharding and just parametrize the number of parallels or other options while not wasting CPU and network hops by these extra Peas

[github-actions]

Latency summary

Current PR yields:

• 😶 index QPS at 1624, delta to last 3 avg.: -1%
• 🐢🐢 query QPS at 31, delta to last 3 avg.: -6%

Breakdown

Version	Index QPS	Query QPS
current	1624	31
0.9.15	1648	33

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

[codecov]

Codecov Report

Merging #1711 (f53633e) into master (2fb2a5e) will decrease coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1711      +/-   ##
==========================================
- Coverage   84.78%   84.73%   -0.06%     
==========================================
  Files         133      133              
  Lines        6856     6857       +1     
==========================================
- Hits         5813     5810       -3     
- Misses       1043     1047       +4     

Impacted Files	Coverage Δ
jina/parsers/peapods/pods/base.py	100.00% <100.00%> (ø)
jina/drivers/querylang/select.py	79.31% <0.00%> (-6.90%)	⬇️
jina/flow/base.py	86.57% <0.00%> (-0.55%)	⬇️

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[florian-hoenicke]

Can we add a small test here?

[JoanFM]

Can we add a small test here?

sure, will

[JoanFM]

Can we add a small test here?

Done!

[nan-wang]

LGTM👍

Done!