Ruru: expose customScalarSchemas so custom scalars aren't flagged as invalid in the variable editor

Problem

Ruru's variable editor (built on @graphiql/react → monaco-graphql → graphql-language-service) flags any custom scalar that holds an object or array as invalid, e.g. for @graphile/postgis's GeoJSON scalar:

{ "type": "Point", "coordinates": [9.5, 51.3] }

produces:

Incorrect type. Expected one of string, number, boolean, integer.

in the variable editor, even though the request executes fine server-side. This affects any plugin author whose input/output types include a custom JSON-like scalar (GeoJSON, arbitrary JSON, etc.), so it is not specific to postgis.

Root cause

Traced fully in graphql/graphiql#4447. Short version: graphql-language-service and monaco-graphql already support overriding the JSON Schema used for a given scalar name (customScalarSchemas), but @graphiql/react - which Ruru renders directly - never exposes this as a prop. I have a patch for @graphiql/react ready: graphql/graphiql#4448.

What Ruru would need, once that lands

Once @graphiql/react accepts customScalarSchemas and a release is out:

• Add customScalarSchemas to RuruProps (ruru-types) and RuruClientConfig/RuruConfig (ruru), following the same Pick<GraphiQLProps, ...> pattern already used for editorTheme, initialVariables, etc.
• Thread it down to wherever the <GraphiQL>/<GraphiQLProvider> instance gets mounted, so it can be set via graphile.config.ts.
• Bump the @graphiql/react dependency to the release containing the new prop.

Happy to send this as a PR too once the upstream piece is merged and released! Opening this as a tracking issue in the meantime since it's blocked on that.

Motivating use case

@graphile/postgis's GeoJSON scalar (see graphile/postgis#66) is exactly this shape: input/output type for geometry/geography columns, holds arbitrary GeoJSON objects.