Allow to modify PinnedMessage in StreamMessageWidget => MessageWidgetContent

[Mounix99]

Please select which package this feature is related to

stream_chat_flutter

Which platforms would this feature impact?

iOS, Android, Web, Windows, MacOS, Linux

Is your feature request related to a problem?

I need to have more control over PinnedMessage widget from your package to been able to customise it

Describe the solution that you'd like

I'd like to have any ways to provide my own PinnedMessage widget to StreamMessageWidget => MessageWidgetContent to replace the default one. Both main and copyWith constructors should have this option

Describe alternatives that you have considered

I don't think there is better alternative

Additional context

No response

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