feat(jaml): add keyword jtype to represent YAML tag

[hanxiao]

Content

• we will be slowly migrating from !YAMLTag to jtype: YAMLTag, this PR is a starting point
• the rationale behind this is we want to enable JSONSchema (FYI, YAML is a superset of JSON) for IDE-level of validation and autocompletion, as we heavily rely on YAML configs.
• the current problem is that those customized tags are not compatible to JSONschema, but also creates problem during internal/external-integration. (@BastinJafari on dashboard)
• in general, we want the maximum compatibility of our YAML file, to get broader support from the Schema ecosystem.

Breaking Changes

• the old way of {"__cls": "SomeExecutor" } to construct executor from JSON is now replaced by {"jtype": "SomeExecutor"}

Alternatives

Other alternatives to realize this but dropped: https://github.com/jina-ai/jina/blob/refactor-jaml-tag-2/

[codecov]

Codecov Report

Merging #2044 (f7c5830) into master (1f4ded9) will decrease coverage by 13.89%.
The diff coverage is 47.50%.

@@             Coverage Diff             @@
##           master    #2044       +/-   ##
===========================================
- Coverage   88.75%   74.86%   -13.90%     
===========================================
  Files         200      181       -19     
  Lines       10933    10373      -560     
===========================================
- Hits         9704     7766     -1938     
- Misses       1229     2607     +1378     

Flag	Coverage Δ
daemon	?
jina	74.86% <47.50%> (-14.33%)	⬇️

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

Impacted Files	Coverage Δ
jina/clients/base.py	75.83% <ø> (-5.00%)	⬇️
jina/executors/indexers/keyvalue.py	98.70% <ø> (ø)
jina/flow/base.py	58.26% <ø> (-34.13%)	⬇️
jina/helloworld/chatbot/__init__.py	89.28% <ø> (ø)
jina/helloworld/helper.py	90.62% <ø> (ø)
jina/helloworld/multimodal/__init__.py	90.90% <ø> (ø)
jina/importer.py	95.60% <ø> (+15.18%)	⬆️
jina/logging/logger.py	77.95% <ø> (-4.73%)	⬇️
jina/logging/profile.py	70.07% <ø> (-25.20%)	⬇️
jina/optimizers/__init__.py	0.00% <ø> (-94.40%)	⬇️
... and 125 more

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[github-actions]

Latency summary

Current PR yields:

• 😶 index QPS at 997, delta to last 3 avg.: +2%
• 😶 query QPS at 16, delta to last 3 avg.: -4%

Breakdown

Version	Index QPS	Query QPS
current	997	16
1.0.4	992	16
1.0.3	945	16

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