Request: .Should().PushAnySatisfying(..)

### Description

Just started using FA.Reactive and it's awesome, great work!

I have a suggestion for an assertion similar to `SatisfyRespectively` for collection assertions: `PushAnySatisfying`

#### Use Case

I am looking for an occurrence of a particular element that satisfies some constraints. I don't care about the ordering, hence the `Any` of `PushAnySatisfying`.

Example usage:

```csharp
observable.Observe()
.Should()
.PushAnySatisfying(e => {
e.Property.Should().Be("value");
e.OtherProperty.Should().Be("other value");
});
```