Set foundation for multiple OpenAPI.json files

[lightwalker-eth]

Background

• In feat(docs): OpenAPI spec sync with CI validation and PR previews #1550 we are advancing a number of goals related to how we work with openapi.json files in relation to ENSApi.
• Currently, our focus and priority in relation to setting the foundation for OpenAPI related work should be constrained only to ENSApi.
• However, we should note how other apps beyond ENSApi in the ENSNode monorepo have APIs that we will want to apply all the same OpenAPI patterns to. This includes ENSIndexer and ENSRainbow. Potentially more future apps as well too, such as the new app that will soon be spun out of ENSApi specifically for ENS Referral Program related APIs. Etc.

Goals

• Set the foundation for supporting multiple openapi.json files from multiple apps.
• Stop making the assumption that we will only ever have a single openapi.json file in the monorepo.

Non-Goals

• For the scope of this issue, we shouldn't actually introduce any new openapi.json files yet! Instead, we should only imagine and prepare for them to exist. We should stay focused on ENSApi for now.

Quick ideas

• Maybe instead of building a single openapi.json file we instead build a distinct openapi.json file for each app with a filename such as {appname}-openapi.json. Advice appreciated.
• The scope of this issue might be solved simply by renaming the openapi.json file that we're building and all the references to it.