chore(docs): replace broken packages link with correct plugins (#12076)
chore(docs): replace broken packages link with correct plugins (#12076)

## Description

This change fixes the broken link reference to the Plugins page in the Gatsby Tutorial Part Four in the "When do I use unstructured data vs GraphQL?" section. It replaces the '/packages/' link ref with '/plugins'.

## Related Issues

Fixes #12029 

ChristopherBiscardi/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,ChristopherBiscardi/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby