Publish v2 /health and /ready readiness-gate API docs on next OSS v2 release

Tracking issue for releasing the updated `/health` and `/ready` API reference docs once the next InfluxDB OSS v2.x ships the readiness-gate behavior.

## Context

[influxdata/influxdb#27370](https://github.com/influxdata/influxdb/pull/27370) added readiness gates and richer `/health` + `/ready` responses to `influxd`. It is **merged to `main-2.x` but unreleased** (docs currently track v2.9.1).

- Spec update: **#7286** — adds the `/ready` `503` response and extends the `Ready` schema (`starting` status + failing-only `checks`). Labeled `release:pending`.
- Source-repo operator doc: [influxdata/influxdb#27477](https://github.com/influxdata/influxdb/pull/27477) — reviewed for style; kept as an in-repo engineering reference (niche audience), not ported to the docs site.

## Tasks

- [ ] Confirm the InfluxDB OSS v2.x version that ships influxdata/influxdb#27370, and rename this milestone to that version.
- [ ] Land the spec change upstream in `influxdata/openapi`, or it will be overwritten on the next `getswagger.sh` regen.
- [ ] When that v2 version releases: flip #7286 `release:pending` → `release:ready`, then review and merge.

Start by confirming which InfluxDB OSS v2.x release includes influxdata/influxdb#27370, then review spec change #7286 and the upstream influxdata/openapi update before the next getswagger.sh regeneration. Done means the milestone names that release, #7286 is marked release:ready, and the updated API documentation is reviewed and merged.

Written by the indexing model from the issue text.