introduce flags for customizing standard providers using their own YA…

[zilin]

Allow customization of standard providers via YAML files

This commit introduces two new command-line flags, --standard_io_yaml_file and --standard_providers_yaml_file, enabling users to customize the standard providers used when executing Apache Beam YAML pipelines.

• --standard_io_yaml_file: Specifies a YAML file containing definitions for standard I/O providers, allowing users to override or extend the default I/O providers.
• --standard_providers_yaml_file: Specifies a YAML file containing definitions for other standard providers (i.e., non-I/O providers), providing similar customization capabilities.

The standard_providers function in yaml_provider.py has been updated to load providers from these user-specified files if provided, falling back to the default standard providers if the flags are not used.

These changes provide greater flexibility and extensibility when defining and running Beam pipelines with YAML, allowing users to tailor the available transforms and I/O connectors to their specific needs.

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[shunping]

@derrickaw could you help to review this? Maybe you have more context on this PR.

[derrickaw]

Hi @shunping, I don't have any context on this part, sorry.

[robertwb]

I have the context here, can be a reviewer.