Define standard `EnsNodeResponse<T>` JSON response schema

[lightwalker-eth]

Goals include: enabling our infrastructure-level fallbacks living in AWS Cloudfront to return JSON-based errors that clients can nicely interpret, such as when we are making an infrastructure-level fallback at the loadbalancer level in Cloudflare on an alpha-style config template (alpha and alpha-sepolia) -- which therefore is not subgraph compatible and we can return some statically defined JSON error.

Currently, in the above situation, we are just returning a simple error message (not formatted as JSON).

We may need additional custom JSON-based fallback errors for GraphQL endpoints as this response schema will likely differ.

[lightwalker-eth]

Above is a screenshot of an API endpoint that's currently under development in #1358

Opportunities for improvement here include:

1. We shouldn't put the main response field at the root-object level in the response. Instead it should be nested under a field such as data: ResponseType.
2. We should move this accurateAsOf field out of the ResponseType and instead move it into the parent generic EnsNodeResponse object whenever the response code is ok / success.

[stevedylandev]

In addition to response schemas with data, there should also be a standardized error schema. See this thread.