GraphQL - validate schema in the control plane so envoy doesn't NACK on invalid gql schema

[saiskee]

Do you have a suggestion for code improvement or tracking existing technical debt? Please describe.

This came up in a customer scenario where: gRPC config for [type.googleapis.com/envoy.config.route.v3.RouteConfiguration](http://type.googleapis.com/envoy.config.route.v3.RouteConfiguration) rejected: error parsing graphql schema: Unknown field type: BigDecimal line: 84 column: 3

the big decimal type was not defined in the schema. While this was an invalid schema, it caused a bad UX because it caused envoy to NACK, causing multiple failures across the system.

Describe the solution you'd like

Validate schemas / maybe other potential envoy graphql nacks in CP before sending config to Envoy.

Additional Context

No response