Swashbuckle.aspnetcore: Added Deep Link support

[niemyjski]

It appears that after the upgrade to swagger 3.0 we lost all deep linking support: https://github.com/swagger-api/swagger-ui/blob/master/docs/usage/deep-linking.md

[domaindrivendev]

I guess it's disabled by default in swagger-ui 3x. You should be able to explicitly enable it with the following:

app.UseSwaggerUI(c =>
{
    ...
    c.EnableDeepLinking();
});