Fixes in command argument in json files
* Fixes BITFIELD's syntax ("sub-commands" can be repeated, and OVERFLOW is only valid for SET and INCR)
* Improves readability of SET (reordered)
* Fixes GEOSEARCH and GEOSEARCH_RO syntices (use `oneof` for mutually exclusive group instead of `optional`)
* Fixes MIGRATE syntax (use `oneof` for mutually exclusive group instead of `optional`)
* Fixes MODULE LOADEX syntax (the `CONFIG` token should be repeated too when using multiple configs)
other:
* make generate-command-help.rb accept a path to commands.json, or read it from stdin (e.g. `generate-commands-json.py | generate-command-help.rb -`)
3e09a8c097