feat(flow): add needs, inspect, version to flow yaml

[hanxiao]

Feature

• Flow YAML now supports versioning. The current master is considered as version: legacy.
• Flow YAML now supports needs, inspect as constructor beyond add, they can be specified via method:

!Flow
version: '1.0'
pods:
  - name: pod0  # notice the change here, name is now an attribute
    method: add  # by default method is always add, available: add, needs, inspect
    uses: _pass
    needs: gateway
  - name: pod1  # notice the change here, name is now an attribute
    method: add  # by default method is always add, available: add, needs, inspect
    uses: _pass
    needs: gateway
  - method: inspect  # add an inspect node on pod1
  - method: needs  # let's try something new in Flow YAML v1: needs
    needs: [pod1, pod0]

• dumper & loader can be specified for each version, see jina.flow.parser for details

[codecov]

Codecov Report

Merging #1442 (6dabc50) into master (ce5f094) will decrease coverage by 0.04%.
The diff coverage is 82.50%.

@@            Coverage Diff             @@
##           master    #1442      +/-   ##
==========================================
- Coverage   81.58%   81.54%   -0.05%     
==========================================
  Files         109      113       +4     
  Lines        6575     6761     +186     
==========================================
+ Hits         5364     5513     +149     
- Misses       1211     1248      +37     

Impacted Files	Coverage Δ
jina/peapods/pods/__init__.py	84.00% <ø> (-0.31%)	⬇️
jina/types/sets/document.py	96.47% <ø> (ø)
jina/flow/yaml_parser/legacy.py	52.63% <52.63%> (ø)
jina/flow/yaml_parser/base.py	75.00% <75.00%> (ø)
jina/flow/yaml_parser/__init__.py	96.29% <96.29%> (ø)
jina/excepts.py	100.00% <100.00%> (ø)
jina/flow/yaml_parser/v1.py	100.00% <100.00%> (ø)
jina/clients/python/grpc.py	66.66% <0.00%> (-14.29%)	⬇️
jina/clients/python/runtime.py	78.33% <0.00%> (-8.34%)	⬇️
jina/logging/sse.py	92.64% <0.00%> (-2.52%)	⬇️
... and 34 more

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