(docs) Consider moving/removing fragments section of GraphQL API

[tesseralis]

Summary

Consider moving the "Fragments" section of the GraphQL API to its own page(s). Alternately, remove these sections, since their content is already covered under the Gatsby Image API.

Motivation

The "Fragments" section contains GraphQL fragments for two plugins: Contentful and ImageSharp. It makes them hard to find when they're hidden at the bottom of the GraphQL API.

Additionally, this requires us to pull in a one-time use MDX component, <GraphQLApiQuery>, which can interfere with translated docs. There are other work-arounds for this, like making the component global

Furthermore, the static-query used is included in the main site bundle for some reason, resulting in significant bloat for the site (#21470). 10% of our main website bundle comes from these queries! Moving them to page queries, or removing them alltogether, alleviates this.

Steps to resolve this issue

• Create a new overview page "GraphQL Fragments" that introduces the concept of fragments and links to the two pages below.
• Create two new pages "Contentful Fragments" and "ImageSharp Fragments", each pulling in the APIs for the specific plugin using the new template-api defined in feat(www): Convert API pages to MDX #20763

Related Issues

Part of: #20795
Depends on: #20763