Update code block in quickstart-app-plugin tutorial to use named import.

Signed-off-by: Brent Sharrow <bsharrow4@gmail.com>

contrib/docs/tutorials/quickstart-app-plugin/ExampleFetchComponent.md

@@ -76,7 +76,7 @@ export const DenseTable = ({ viewer }: DenseTableProps) => {
   );
 };
 
-const ExampleFetchComponent = () => {
+export const ExampleFetchComponent = () => {
   const auth = useApi(githubAuthApiRef);
 
   const { value, loading, error } = useAsync(async (): Promise<any> => {
@@ -106,6 +106,4 @@ const ExampleFetchComponent = () => {
     />
   );
 };
-
-export default ExampleFetchComponent;
 ```

docs/tutorials/quickstart-app-plugin.md

@@ -146,11 +146,9 @@ import {
 } from '@backstage/core';
 import { graphql } from '@octokit/graphql';
 
-const ExampleFetchComponent = () => {
+export const ExampleFetchComponent = () => {
   return <div>Nothing to see yet</div>;
 };
-
-export default ExampleFetchComponent;
 ```
 
 3. Save that and ensure you see no errors. Comment out the unused imports if