Indicate in the schema whether fields are optional or not

[Shadow53]

I'm trying to generate a Rust client for butlerd. I've run into an issue where the schema does not make obvious whether certain fields are optional or not. The documentation may mention it, but that is not reliable to parse programmatically.

I know and appreciate that Go's "zero" values by default thing may make this difficult. I figure a good starting point would be marking all *T as optional and T as required, for actual types T. This will help me determine whether to generate the field as T or Option<T>.

[Shadow53]

Just saw that #220 exists. That looks roughly like what I'm looking for, though I can't validate the current implementation.