docs: Add missing docs for alloc restart api

website/source/api/allocations.html.md

@@ -649,3 +649,46 @@ $ curl -X POST -d '{"Signal": "SIGUSR1" }' \
 ```json
 {}
 ```
+
+## Restart Allocation
+
+This endpoint restarts an allocation or task in-place.
+
+| Method | Path                       | Produces                   |
+| ------ | -------------------------- | -------------------------- |
+| `POST` / `PUT`  | `/v1/allocation/:alloc_id/restart` | `application/json`         |
+
+The table below shows this endpoint's support for
+[blocking queries](/api/index.html#blocking-queries) and
+[required ACLs](/api/index.html#acls).
+
+| Blocking Queries | ACL Required         |
+| ---------------- | -------------------- |
+| `NO`            | `namespace:alloc-lifecycle` |
+
+### Parameters
+
+- `:alloc_id` `(string: <required>)`- Specifies the UUID of the allocation. This
+  must be the full UUID, not the short 8-character one. This is specified as
+  part of the path.
+
+### Sample Payload
+
+```json
+{
+  "Task": "FOO"
+}
+```
+
+### Sample Request
+
+```text
+$ curl -X POST -d '{"Task": "redis" }' \
+    https://localhost:4646/v1/client/allocation/5456bd7a-9fc0-c0dd-6131-cbee77f57577/restart
+```
+
+### Sample Response
+
+```json
+{}
+```