feat(jaml): allow loading from flatten Flow yaml

[hanxiao]

This enables the loading from a "flattened" Flow YAML, e.g.

jtype: Flow
version: '1'
pods:
  - uses:
    jtype: CustomizedEncoder
    requests:
      on:
        IndexRequest:
          - jtype: FilterQL
            with:
              lookups: { modality__in: [ mode2 ] }
              traversal_paths: [ 'c' ]
          - jtype: EncodeDriver
            with:
              method: encode
              traversal_paths: [ 'c' ]
  - uses: _index
  - uses:
    jtype: BaseEncoder
    metas:
      name: test_indexer
      workspace: ./indexed

[codecov]

Codecov Report

Merging #2216 (a456007) into master (3879045) will decrease coverage by 1.98%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2216      +/-   ##
==========================================
- Coverage   90.51%   88.53%   -1.99%     
==========================================
  Files         208      208              
  Lines       11221    11226       +5     
==========================================
- Hits        10157     9939     -218     
- Misses       1064     1287     +223     

Flag	Coverage Δ
daemon	50.26% <55.55%> (-0.01%)	⬇️
jina	88.85% <100.00%> (-2.13%)	⬇️

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

Impacted Files	Coverage Δ
jina/parsers/helloworld.py	98.21% <ø> (-0.04%)	⬇️
jina/jaml/__init__.py	96.37% <100.00%> (+0.11%)	⬆️
jina/jaml/parsers/flow/v1.py	48.14% <0.00%> (-44.45%)	⬇️
jina/clients/asyncio.py	50.00% <0.00%> (-40.63%)	⬇️
jina/flow/base.py	60.86% <0.00%> (-31.72%)	⬇️
jina/jaml/parsers/flow/legacy.py	22.72% <0.00%> (-20.46%)	⬇️
jina/flow/mixin/async_crud.py	44.59% <0.00%> (-14.87%)	⬇️
jina/flow/asyncio.py	75.00% <0.00%> (-12.50%)	⬇️
jina/jaml/helper.py	87.02% <0.00%> (-6.88%)	⬇️
jina/jaml/parsers/__init__.py	93.61% <0.00%> (-6.39%)	⬇️
... and 12 more

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[github-actions]

Latency summary

Current PR yields:

• 😶 index QPS at 1008, delta to last 3 avg.: -4%
• 😶 query QPS at 17, delta to last 3 avg.: -3%

Breakdown

Version	Index QPS	Query QPS
current	1008	17
1.0.12	1057	17

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