Add `Hint` support to beforeSend and Event processors

Hi, Sentry is great! I am however missing a way to add an attachment to an outgoing event in the BeforeSend callback. For example:

using var host = Host.CreateDefaultBuilder()
    .ConfigureLogging((context, builder) =>
    {
        builder.AddSentry(options =>
        {
            options.BeforeSend = sentryEvent =>
            {
                sentryEvent.AddBreadcrumb("Hello"); // I can do this
                sentryEvent.AddAttachment("Foo.txt"); // But I cannot do this
                return sentryEvent;
            };
        };
    })
    .Build();

Am I missing something, or this is a missing feature?

[mattjohnsonpint]

Because we’ve currently implemented BeforeSend as a property that accepts a delegate function, there’s no clean way to add a Hint parameter to the function without making a breaking change that would require a major version bump. Methods are overloadable, but properties are not.

I’d like to handle this as follows:

public class SentryOptions
{
    // ...

    internal Func<SentryEvent, Hint, SentryEvent?>? _beforeSend;

    public void SetBeforeSend(Func<SentryEvent, SentryEvent?> beforeSend)
    {
        _beforeSend = (e, _) => beforeSend(e);
    }

    public void SetBeforeSend(Func<SentryEvent, Hint, SentryEvent?> beforeSend)
    {
        _beforeSend = beforeSend;
    }

    [Obsolete("This property will be removed in a future version. Use SetBeforeSend instead.")]
    public Func<SentryEvent, SentryEvent?>? BeforeSend
    {
        get => null;
        set => _beforeSend = value is null ? null : (e, _) => value(e);
    }

    // ...
}

The usage would then change from:

options.BeforeSend = @event => { ... };

To the following:

options.SetBeforeSend(@event => { ... });

… or when hints are desired:

options.SetBeforeSend((@event, hint) => { ... });

[mattjohnsonpint]

Note, this also applies to BeforeBreadcrumb, and our docs already (incorrectly) state that hints are supported.

https://docs.sentry.io/platforms/dotnet/configuration/options/#before-breadcrumb