docs: update icons on existing react quickstart guide (#0) (#1968)

Author: avarobinson

docs/pages/react/quickstart/existing-project.mdx

@@ -235,20 +235,19 @@ export default function Home() {
 Now that you have basic authentication working, you can explore additional features:
 
 <CardGroup cols={2}>
-  <Card title="Send User Operations" icon={<img src="https://static.alchemyapi.io/images/docs/right_arrow.svg" alt="Send User Operations"/>} href="/wallets/transactions/send/send-user-operations">
+  <Card
+    title="Send User Operations"
+    icon="bolt"
+    href="/wallets/transactions/send/send-user-operations"
+  >
     Learn how to perform transactions by sending user operations with your smart wallet.
   </Card>
 
 {" "}
 
 <Card
   title="Customize UI Components"
-  icon={
-    <img
-      src="https://static.alchemyapi.io/images/docs/right_arrow.svg"
-      alt="Customize UI"
-    />
-  }
+  icon="fa-solid fa-pencil"
   href="/wallets/react/ui-components"
 >
   Customize and style the UI components to match your application's design.
@@ -258,18 +257,17 @@ Now that you have basic authentication working, you can explore additional featu
 
 <Card
   title="Add Gas Sponsorship"
-  icon={
-    <img
-      src="https://static.alchemyapi.io/images/docs/right_arrow.svg"
-      alt="Gas Sponsorship"
-    />
-  }
+  icon="gas-pump"
   href="/wallets/transactions/sponsor-gas/sponsor-gas"
 >
   Enable gasless transactions by setting up gas sponsorship for your users.
 </Card>
 
-  <Card title="Multi-Factor Authentication" icon={<img src="https://static.alchemyapi.io/images/docs/right_arrow.svg" alt="MFA"/>} href="/wallets/react/mfa/setup-mfa">
+  <Card
+    title="Multi-Factor Authentication"
+    icon="shield"
+    href="/wallets/react/mfa/setup-mfa"
+  >
     Enhance security by implementing multi-factor authentication for your users.
   </Card>
 </CardGroup>