Merge `/api/config` into `/api/indexing-status`

[tk-o]

We have an opportunity to simplify how clients interact with ENSApi.

Currently, a source of complexity for ENSNode clients is a need to separately request both the config and indexing status and to manage all the possible error states where one request succeeds or the other doesn't (i.e. request times out). Then, the next step for the client is to ensure both data models are consistent with each other for example, chains from the config match the chains in the indexing status.

To address such complexities, ENSApi should combine both the indexing status and config data models into a single API endpoint that returns both together.

Goals

• Merge /api/config data model into /api/indexing-status data model by adding ensApiPublicConfig field to IndexingStatusResponseOk type.

Non-goals

• ENSIndexer APIs must remain unchanged.

[lightwalker-eth]

@tk-o Suggest that before we execute this goal we should first optimize the config API and data model to be really mature and optimally future-proofed. There's some open GitHub issues related to optimizing the config API. Let's close all those first before we proceed here.