fix(commands): retrieve localization key for subcommand groups from docstring

[shiftinv]

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Summary

While the docstring of subcommand groups is largely useless (as descriptions of subcommand groups are not exposed in the UI anywhere), it should still be parsed to retrieve localization key for the group name, if any.

see also: https://canary.discord.com/channels/808030843078836254/1337797831347671122

Checklist

• [x] If code changes were made, then they have been tested
  • [ ] I have updated the documentation to reflect the changes
  • [x] I have formatted the code properly by running pdm lint
  • [x] I have type-checked the code by running pdm pyright
• [x] This PR fixes an issue
• [ ] This PR adds something new (e.g. new method or parameters)
• [ ] This PR is a breaking change (e.g. methods or parameters removed/renamed)
• [ ] This PR is not a code change (e.g. documentation, README, ...)