Link to PCE blog post from the docs

[nikolasburk]

There should be several links from the PCE docs pages to the blog post:

• Root (https://www.prisma.io/docs/concepts/components/prisma-client/client-extensions): Add a note to the intro with a link to the blog post, mentioning that it contains a lot of practical examples
• Go through the various docs pages for PCE and find relevant places where to link specific examples of the blog post