Add validation to `@ChainKey` to prevent utf 0 in keys

[dzikowski]

suggested changes:

export interface ChainKeyMetadata extends ChainKeyConfig {
  key: string | symbol;
+ allowUtf0?: boolean
}

export function ChainKey(chainKeyConfig: ChainKeyConfig): PropertyDecorator {
  return (target, key) => {
    const fields: ChainKeyMetadata[] = Reflect.getOwnMetadata("galachain:chainkey", target) || [];

    const existingField = fields.find((field) => field.position === chainKeyConfig.position);

+   // inject somewhere a validation decotator to fail on utf0

    if (existingField === undefined) {
      fields.push({ key, ...chainKeyConfig });
      Reflect.defineMetadata("galachain:chainkey", fields, target);
    }
  };
}