hermes config 0.4 compatibility

[greg-szabo]

Closes: #1039

Description

gm creates hermes 0.4 (master) compatible configuration

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For contributor use:

• Updated the Unreleased section of CHANGELOG.md with the issue.
• If applicable: Unit tests written, added test to CI.
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Updated relevant documentation (docs/) and code comments.
• Re-reviewed Files changed in the Github PR explorer.

[adizere]

Two further improvements I can see:

• Update the .toml file used in example section of the readme.md. Maybe to reduce the amount of config information that needs to be maintained, instead of using a dedicated .toml file in that example, use the default one scripts/gm/gm.toml.

• The command gm hermes config should ideally not overwrite Hermes's current values in its configuration file, in particular for fields strategy and log_level. I think gm v0.02 was correctly loading the config values and did not overwrite these fields, but these changes in v0.0.3 introduced the overwriting issue.

But these are both minor feature requests, not a priority, so let's leave them for subsequent PRs.