chore: migrated API Playground to using the V2 API Definition typings

[abvthecity]

This PR is a follow-up to #1552

Instead of calling /api/fern-docs/resolve-api, which resolves all endpoints, websockets, and webhooks across all the api definitions, this PR introduces 3 new getter functions:

• GET /api/fern-docs/api-definition/{api}/endpoint/{endpointid} (link)
• GET /api/fern-docs/api-definition/{api}/websocket/{websocketid} (link)
• GET /api/fern-docs/api-definition/{api}/webhook/{webhookid} (link)

Each of these endpoints:

1. loads the api definition from the the api.v1.read endpoint instead of docs.v2.read, which reduces the payload size transferred from FDR to NextJS.
2. prune the api definition to the specific endpoint that is being requested
3. resolve and cache all api definition descriptions using the new Transformer utility.

In the API Playground,

• all references to ResolvedApiDefinition types have been removed in favor of the fdr-sdk types.
• endpoint definition + endpoint node + types are wrapped in a EndpointContext, which makes it easier to pass the context down to its children without specifying each of the parameters separately. This is useful because an endpoint node and endpoint definition is always paired together.
• useSWRImmutable is used to leverage SWR's cache
• the PlaygroundEndpointSelector is configured so that hovering over endpoints will trigger a prefetch, improving perceived speed.

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Caching

• ApiDefinitionLoader: link does the bulk of the load -> prune -> cache work in the load() method, and the resolveDescriptions() method.

• ApiDefinitionCache: link shows how we leverage mset and mget to batch setting api definitions to parallelize and reduce server round-trips.

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• tested on flagright (ensure that application/json on multipart form is retained)

[dsinghvi]

Blind +1

[RohinBhargava]

@abvthecity, can we bring this back?