Docs: Fix API document (#9210)

**What this PR does / why we need it**:

Remove /ready and /metrics from API list of the querier and the query
frontend because they are exposed by all components.

Remove /loki/api/v1/push from API list of the querier and the query
frontend because it is exposed by distributor.

Move /api/prom/push from API list of the querier and the query frontend
to API list of the distributor because it is exposed by distributor.

Add /api/prom/series to API list of the querier and the query frontend.

Change reference to /loki/api/v1/label to /loki/api/labels because
former is not documented.

**Which issue(s) this PR fixes**:

**Special notes for your reviewer**:

**Checklist**
- [x] Reviewed the
[`CONTRIBUTING.md`](https://github.com/grafana/loki/blob/main/CONTRIBUTING.md)
guide (**required**)
- [ ] Documentation added
- [ ] Tests updated
- [ ] `CHANGELOG.md` updated
- [ ] Changes that require user attention or interaction to upgrade are
documented in `docs/sources/upgrading/_index.md`

Signed-off-by: Mitsuru Kariya <mitsuru.kariya@nttdata.com>

docs/sources/api/_index.md

@@ -34,18 +34,17 @@ These endpoints are exposed by the querier and the query frontend:
 - [`GET /loki/api/v1/series`](#list-series)
 - [`GET /loki/api/v1/index/stats`](#index-stats)
 - [`GET /loki/api/v1/tail`](#stream-log-messages)
-- [`GET /ready`](#identify-ready-loki-instance)
-- [`GET /metrics`](#return-exposed-prometheus-metrics)
 - **Deprecated** [`GET /api/prom/tail`](#get-apipromtail)
 - **Deprecated** [`GET /api/prom/query`](#get-apipromquery)
 - **Deprecated** [`GET /api/prom/label`](#get-apipromlabel)
 - **Deprecated** [`GET /api/prom/label/<name>/values`](#get-apipromlabelnamevalues)
-- **Deprecated** [`POST /api/prom/push`](#post-apiprompush)
+- **Deprecated** [`GET /api/prom/series`](#list-series)
 
 These endpoints are exposed by the distributor:
 
 - [`POST /loki/api/v1/push`](#push-log-entries-to-loki)
 - [`GET /distributor/ring`](#display-distributor-consistent-hash-ring-status)
+- **Deprecated** [`POST /api/prom/push`](#post-apiprompush)
 
 These endpoints are exposed by the ingester:
 
@@ -1346,7 +1345,7 @@ $ curl -G -s  "http://localhost:3100/api/prom/label/foo/values" | jq
 
 ### `GET /api/prom/label`
 
-> **WARNING**: `/api/prom/label` is DEPRECATED; use `/loki/api/v1/label`
+> **WARNING**: `/api/prom/label` is DEPRECATED; use `/loki/api/v1/labels`
 
 `/api/prom/label` retrieves the list of known labels within a given time span. It
 accepts the following query parameters in the URL: