Allow to configure restrictedToMinimumLevel via LoggingLevelSwitch

[zvirja]

While configuring a sink in Serilog, it's possible to pass both static LogEventLevel, but also the LoggingLevelSwitch to control the value dynamically. It gives a bit of flexibility. Unfortunately, as of now the config.WriteTo.Seq(..) API doesn't allow to pass the value.

In this PR I just introduce the parameter, so it's possible to use both static and dynamic value.

[nblumhardt]

Thanks for sending this. I think the omission was deliberate, because of possible confusion with the controlLevelSwitch parameter accepted by the method. We should review this, as they're distinct, but there are some binary compatibility requirements around this method signature we'll also need to think through, so this could take a little while.

In the meantime, one possible workaround would be:

    .WriteTo.Conditional(
        evt => levelSwitch.IsEnabled(evt.Level),
        wt => wt.Seq(...))

[zvirja]

@nblumhardt wow, thanks for the suggestion! it works perfectly fine for me.

Yet I think we should have the API I am suggesting in this PR. Primarily, to be on par with e.g. .ApplicationInsights() - they have both in their API. This way people would be less surprised and code more following POLA.

As for the breaking change - well, you know better your policies. But feels like it could be just enough to bump the major and have compilation-time compatibility. There is always as well a possibility to just introduce an overload. But you are smart people, you are aware of all of this 😉 So please take your time.

Thanks for the fast reply!