refactor: move save/load config to JAML module

[hanxiao]

Details see docstring

Support substitutions in YAML:
- Environment variables: ${{ENV.VAR}} (recommended), ${{VAR}}, $VAR.
- Context dict (context): ${{VAR}}(recommended), $VAR.
- Internal reference via this and root: ${{this.same_level_key}}, ${{root.root_level_key}}

    Substitutions are carried in the order and multiple passes to resolve variables with best effort.

    .. highlight:: yaml
    .. code-block:: yaml

        !BaseEncoder
        metas:
            name: ${{VAR_A}}  # env or context variables
            workspace: my-${{this.name}}  # internal reference

    .. highlight:: python
    .. code-block:: python

        # load Executor from yaml file
        BaseExecutor.load_config('a.yml')

        # load Executor from yaml file and substitute environment variables
        os.environ['VAR_A'] = 'hello-world'
        b = BaseExecutor.load_config('a.yml')
        assert b.name == hello-world

        # load Executor from yaml file and substitute variables from a dict
        b = BaseExecutor.load_config('a.yml', context={'VAR_A': 'hello-world'})
        assert b.name == hello-world

        # disable substitute
        b = BaseExecutor.load_config('a.yml', substitute=False)

[github-actions]

Latency summary

Current PR yields:

• 😶 index QPS at 1728, delta to last 3 avg.: -1%
• 😶 query QPS at 27, delta to last 3 avg.: -5%

Breakdown

Version	Index QPS	Query QPS
current	1728	27
0.8.12	1755	28
0.8.11	1726	28
0.8.10	1775	28

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

[codecov]

Codecov Report

Merging #1533 (7cd3c34) into master (d45af86) will increase coverage by 0.24%.
The diff coverage is 96.52%.

@@            Coverage Diff             @@
##           master    #1533      +/-   ##
==========================================
+ Coverage   84.35%   84.60%   +0.24%     
==========================================
  Files         109      108       -1     
  Lines        6277     6359      +82     
==========================================
+ Hits         5295     5380      +85     
+ Misses        982      979       -3     

Impacted Files	Coverage Δ
jina/executors/compound.py	85.60% <ø> (ø)
jina/logging/logger.py	82.25% <ø> (+0.14%)	⬆️
jina/jaml/__init__.py	95.65% <94.52%> (+1.31%)	⬆️
jina/jaml/helper.py	94.01% <98.48%> (+5.78%)	⬆️
jina/enums.py	96.52% <100.00%> (+0.09%)	⬆️
jina/excepts.py	100.00% <100.00%> (ø)
jina/flow/base.py	89.03% <100.00%> (-0.14%)	⬇️
jina/jaml/parsers/executor/legacy.py	87.09% <100.00%> (+0.21%)	⬆️
jina/logging/profile.py	68.33% <0.00%> (-0.58%)	⬇️
jina/drivers/craft.py	100.00% <0.00%> (ø)
... and 20 more

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