Add an Add(this IList<...> IParameterModelConvention) extension method

[rynowak]

Looks like we missed this one in https://github.com/aspnet/Mvc/blob/dev/src/Microsoft.AspNetCore.Mvc.Core/DependencyInjection/ApplicationModelConventionExtensions.cs

You can add an application/controller/action convention to MvcOptions.Conventions but not a parameter convention. Found while discussing docs.