animation.startup setting is missing

Set `animation: {"startup": true} `- setting this in your options will cause your chart to start with series values drawn at the baseline, and animate out to their final state.

Added with:

**Configuration.fs (line 8)**
```js
type Animation() =

let mutable durationField : int option = None
let mutable easingField : string option = None
let mutable startUpField : bool option = None

member __.startup
with get() = startUpField.Value
and set(value) = startUpField <- Some value

member __.duration
with get() = durationField.Value
and set(value) = durationField <- Some value

member __.easing
with get() = easingField.Value
and set(value) = easingField <- Some value

member __.ShouldSerializeduration() = not durationField.IsNone
member __.ShouldSerializeeasing() = not easingField.IsNone
member __.ShouldSerializestartup() = not startUpField.IsNone
```

Start in Configuration.fs around line 8 and inspect the Animation configuration alongside duration and easing. Add support for the startup setting and its serialization behavior as shown in the issue, then verify that animation: {"startup": true} is accepted and emitted in chart options.

Written by the indexing model from the issue text.