feat(graphql): replace deprecated graphql-playground with graphiql

[Patrickroelofs]

What?

This PR replaces the deprecated graphql-playground interface with the modern graphiql IDE for exploring and testing the GraphQL API.

Why?

graphql-playground was officially retired by the GraphQL Foundation in 2020 and has been unmaintained for several years, which introduces dependency drift and potential security vulnerabilities. graphql/graphql-playground#1143 graphiql is the actively maintained, official standard. It offers a more modern developer experience, better accessibility, and up-to-date dependencies.

Besides that graphql-playground has severe issues in firefox like autocomplete helpers not dissapearing

graphql/graphql-playground#1429

How?

• Removed the old graphql-playground dependencies and related rendering code.
• Added graphiql as the new interactive GraphQL IDE.
• Updated the route handler serving the GraphQL UI to render the new GraphiQL interface while maintaining the same endpoint path.
• Added tests to cover non-existing tests for the playground
• I've kept "graphql playground" naming in docs and routes and only updated to "GraphiQL IDE" where necessary. Playground is such a generic term i feel it fits better and is more descriptive. It also makes it so this has no breaking changes.

Disclosure

• Github Copilot was used during the development of this replacement

Validations

• Tested manually in a latest version payload application and the monorepo dev-mode.