RN: Adds feedback widget theme documentation (#13513)

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⚠️ PR Chain:
- #13512
- 👉  #13513
- #13515

## DESCRIBE YOUR PR
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please link it so it closes automatically.*

Adds feedback widget theme documentation.


Part of getsentry/sentry-react-native#4302

Implementation PR:
getsentry/sentry-react-native#4677

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Should be merged after
getsentry/sentry-react-native#4726 is released

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---------

Co-authored-by: LucasZF <lucas-zimerman1@hotmail.com>
Co-authored-by: Krystof Woldrich <31292499+krystofwoldrich@users.noreply.github.com>

Author: 3 people

docs/platforms/react-native/user-feedback/configuration/index.mdx

@@ -247,3 +247,46 @@ Sentry.feedbackIntegration({
     onAddScreenshot={handleChooseImage}
 });
 ```
+
+## Theming
+
+You can also customize the Feedback Widget colors to match your app's theme. The example below shows how to customize the widget background and foreground for the light and dark system themes with the `feedbackIntegration`.
+
+```javascript
+import * as Sentry from "@sentry/react-native";
+
+Sentry.init({
+  integrations: [
+    Sentry.feedbackIntegration({
+      colorScheme: 'system',
+      themeLight: {
+        foreground: '#ff0000',
+        background: '#00ff00',
+      },
+      themeDark: {
+        foreground: '#00ff00',
+        background: '#ff0000',
+      },
+    }),
+  ],
+});
+```
+
+The available theme options are:
+
+| Key           | Type                        | Default    | Description                                              |
+| ------------- | ----------------------------| ---------- | -------------------------------------------------------- |
+| `colorScheme` | `"system", "light", "dark"` | `"system"` | The color theme. "system" will use your OS color scheme. |
+| `themeLight`  | Feedback Widget Theme       | -          | The light color scheme.                                  |
+| `themeDark`   | Feedback Widget Theme       | -          | The dark color scheme.                                   |
+
+For each theme you can set the following colors:
+
+| Key                | Description                             |
+| ------------------ | ----------------------------------------| 
+| `background`       | Background color for surfaces.          |
+| `foreground`       | Foreground color (i.e. text color).     |
+| `accentForeground` | Foreground color for accented elements. |
+| `accentBackground` | Background color for accented elements. |
+| `border`           | Border color.                           |
+| `feedbackIcon`     | Color for feedback icon.                |