[Command Validation] Allow 0 as valid command value

[maxekman]

Is your feature request related to a problem? Please describe.
Sometimes it's valid to have 0 as a valid command value, as checked by CheckCommand().

Describe the solution you'd like
Would be useful to have an additional struct field to allow 0 as a valid command value: eh:”optional,allow_zero”

Describe alternatives you've considered
To always allow 0, but that would break existing API usage.

Additional context

eventhorizon/command_check.go

Line 97 in 558bc83

// Don't check for zero for value types: