[docs] created spinner documentation (#2758)

Co-authored-by: Shivang Tiwari <shivangtiwari@Shivangs-MacBook-Pro.local>

docs/docs/widgets/spinner.md

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+# Spinner
+
+Spinner widget can be used to provide a visual indication that an action is in progress by awaiting a change.
+
+<div style={{textAlign: 'center'}}>
+
+![ToolJet - Widget Reference - Number Input](/img/widgets/spinner/spinner.png)
+
+</div>
+
+
+## Layout
+
+### Show on desktop
+
+Toggle on or off to display the widget in desktop view. You can programmatically determing the value by clicking on `Fx` to set the value `{{true}}` or `{{false}}`.
+### Show on mobile
+
+Toggle on or off to display the widget in mobile view. You can programmatically determing the value by clicking on `Fx` to set the value `{{true}}` or `{{false}}`.
+
+## Styles
+
+
+### Visibility
+
+Toggle on or off to control the visibility of the widget. You can programmatically change its value by clicking on the `Fx` button next to it. If `{{false}}` the widget will not be visible after the app is deployed. By default, it's set to `{{true}}`.
+
+### Color
+
+Change the color of the Spinner by entering the `Hex color code` or choosing a color of your choice from the color-picker. 
+
+### Size
+
+Change the size of the Spinner by selecting options from the dropdown. It has small and large sizes available.