[Feat]: Add an article on the graphql playground feature

[andaaron]

Is your feature request related to a problem? Please describe.

Examples of search queries which can be used with the search (graphql) endpoint:
https://github.com/project-zot/zot/blob/main/pkg/extensions/search/search.md

The queries can be made from shell (see examples above) or from a UI, such as the graphql playground, or postman.
The graphql playground is available in zot built with the 'debug' build label, and reachable at: /v2/_zot/debug/graphql-playground#

Describe the solution you'd like

Add an article on how to use the graphql playground (should this be for developers?).

Describe alternatives you've considered

No response

Additional context

No response