Convert blog cover images to next/image (#42908)

## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm build && pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)

examples/blog-starter/components/cover-image.tsx

@@ -1,5 +1,6 @@
 import cn from 'classnames'
 import Link from 'next/link'
+import Image from 'next/image'
 
 type Props = {
   title: string
@@ -9,12 +10,14 @@ type Props = {
 
 const CoverImage = ({ title, src, slug }: Props) => {
   const image = (
-    <img
+    <Image
       src={src}
       alt={`Cover Image for ${title}`}
       className={cn('shadow-sm', {
         'hover:shadow-lg transition-shadow duration-200': slug,
       })}
+      width={1300}
+      height={630}
     />
   )
   return (