Card(Props): support for different levels of elevation (shadow)

[reinaldosimoes]

Is your feature request related to a problem? Please Describe.
The Card component works fine for most cases, but it would be cool to have a little bit more customization when it comes to the levels of elevation, either for UX reasons, or just to follow an already set design. The values for shadow would take into consideration Google's Material Design documentation and Apple's Human Interface Guidelines.

Describe the solution you'd like
Introducing a shadow prop with options for how elevated the Card component should be, with "xs" being the current shadow, and the default if shadow is not defined.

shadow: = "xs" | "sm" | "md" | "lg"

Usage

<Card shadow="sm">
  <Card.Image source={require('../image.png')} />
  <Text>Hello World!</Text>
</Card>

[pranshuchittora]

I thought of that before but considering the overall design aspects of other components, it won't be a good fit.
If a user wants to add shadow he can easily do so by adding the containerStyle prop

You can try this out in the RNE Playground -> https://react-native-elements.js.org/#/card

Copy and Paste the following code 👇 in the Playground

import * as React from "react";
import { Card } from "react-native-elements";
import { View, Image } from "react-native";

export default () => {
  return (
    <Card
      containerStyle={{
        shadowColor: "#0002",
        shadowOffset: { width: 0, height: 10 },
        shadowOpacity: 1,
        shadowRadius: 20
      }}
      wrapperStyle={{}}
    >
      <Card.Title>CARD WITH DIVIDER</Card.Title>
      <Card.Divider />
      <View
        style={{
          position: "relative",
          alignItems: "center"
        }}
      >
        <Image
          style={{ width: "100%", height: 100 }}
          resizeMode="contain"
          source={{
            uri:
              "https://avatars0.githubusercontent.com/u/32242596?s=460&u=1ea285743fc4b083f95d6ee0be2e7bb8dcfc676e&v=4"
          }}
        />
        <Text>Pranshu Chittora</Text>
      </View>
    </Card>
  );
}

[reinaldosimoes]

I see the possibility of using this based on the platform, but for consistency, it might not be the best approach.