certain global CLI arguments may be read from env vars

[rnbguy]

Summary

We should allow certain CLI arguments to be read from environment variables.

Problem Definition

When executing hermes-sdk CLI in an environment, we may want to pass some certain repetitive CLI arguments via pre-assigned environment variables to avoid passing them as CLI argument every time.

Proposal

For example, for config file, currently we have to pass it every time.

hermes-sdk --config my_config.toml subcommand1
hermes-sdk --config my_config.toml subcommand2
...

But with an environment variable, we don't have to pass it every time.

HERMES_SDK_CONFIG=my_config.toml

hermes-sdk subcommand1
hermes-sdk subcommand2

Acceptance Criteria

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For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate milestone (priority) applied
• Appropriate contributors tagged
• Contributor assigned/self-assigned