Go generator template: unexport types

[sahidvelji]

These types should not be exported as they are not needed outside of the generated code/package:

cli/internal/generators/golang/golang.tmpl

Lines 10 to 19 in f260209

	type BooleanProvider func(ctx context.Context, evalCtx openfeature.EvaluationContext) (bool, error)
	type BooleanProviderDetails func(ctx context.Context, evalCtx openfeature.EvaluationContext) (openfeature.BooleanEvaluationDetails, error)
	type FloatProvider func(ctx context.Context, evalCtx openfeature.EvaluationContext) (float64, error)
	type FloatProviderDetails func(ctx context.Context, evalCtx openfeature.EvaluationContext) (openfeature.FloatEvaluationDetails, error)
	type IntProvider func(ctx context.Context, evalCtx openfeature.EvaluationContext) (int64, error)
	type IntProviderDetails func(ctx context.Context, evalCtx openfeature.EvaluationContext) (openfeature.IntEvaluationDetails, error)
	type StringProvider func(ctx context.Context, evalCtx openfeature.EvaluationContext) (string, error)
	type StringProviderDetails func(ctx context.Context, evalCtx openfeature.EvaluationContext) (openfeature.StringEvaluationDetails, error)
	type ObjectProvider func(ctx context.Context, evalCtx openfeature.EvaluationContext) (any, error)
	type ObjectProviderDetails func(ctx context.Context, evalCtx openfeature.EvaluationContext) (openfeature.InterfaceEvaluationDetails, error)