Use npx and pnpx in CLI next steps instead of npm and pnpm

[ghost]

Closes: #4272

What are the changes and their implications?

This PR changes the blitz new CLI to mention the correct run commands once the app is built:

npx blitz dev
pnpx blitz dev

// instead of

npm blitz dev
pnpm blitz dev

It does this by using replace().

Bug Checklist

• Changeset added (run pnpm changeset in the root directory)
• Integration test added (see test docs if needed)

Feature Checklist

• Changeset added (run pnpm changeset in the root directory)
• Integration test added (see test docs if needed)
• Documentation added/updated (submit PR to blitzjs.com repo main branch)

[changeset-bot]

⚠️ No Changeset found

Latest commit: 6cc1758

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

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[siddhsuresh]

Closing based on #4272 (comment)