[Community] Update CODE_OF_CONDUCT.md

[parano]

Description

• Update to the latest version of Contributor Covenant https://www.contributor-covenant.org/version/2/0/code_of_conduct/
• Updated the bentoml developers' email address to bentoml-dev@googlegroups.com (I will be inviting active contributors to the list soon)

Motivation and Context

How Has This Been Tested?

Types of changes

• Breaking change (fix or feature that would cause existing functionality to change)
• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Documentation
• Test, CI, or build
• None

Components (if applicable)

• BentoService (model packaging, dependency management, handler definition)
• Model Artifact (model serialization, multi-framework support)
• Model Server (mico-batching, logging, metrics, tracing, benchmark, OpenAPI)
• YataiService (model management, deployment automation)
• Documentation

Checklist:

• My code follows the bentoml code style, both ./dev/format.sh and
  ./dev/lint.sh script have passed
  (instructions).
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• My change requires a change in bentoml/gallery example notebooks
• I have sent a pull request to bentoml/gallery to make that change

[codecov]

Codecov Report

Merging #788 into master will increase coverage by 0.14%.
The diff coverage is 60.10%.

@@            Coverage Diff             @@
##           master     #788      +/-   ##
==========================================
+ Coverage   55.53%   55.68%   +0.14%     
==========================================
  Files         108      114       +6     
  Lines        8144     8336     +192     
==========================================
+ Hits         4523     4642     +119     
- Misses       3621     3694      +73     

Impacted Files	Coverage Δ
bentoml/clipper/__init__.py	0.00% <ø> (ø)
bentoml/yatai/proto/__init__.py	100.00% <ø> (ø)
bentoml/yatai/proto/deployment_pb2.py	100.00% <ø> (ø)
bentoml/yatai/proto/status_pb2.py	100.00% <ø> (ø)
bentoml/yatai/proto/yatai_service_pb2.py	100.00% <ø> (ø)
bentoml/handlers/adapter/dataframe_output.py	27.11% <27.11%> (ø)
bentoml/yatai/proto/yatai_service_pb2_grpc.py	42.20% <37.62%> (+13.03%)	⬆️
bentoml/handlers/json_handler.py	54.54% <45.45%> (+5.17%)	⬆️
bentoml/handlers/tensorflow_tensor_handler.py	70.00% <58.33%> (-2.00%)	⬇️
bentoml/handlers/adapter/tf_tensor_output.py	63.63% <63.63%> (ø)
... and 19 more

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