feat: Add "Speeding up migrations" section to "State persistence" (#1365)

We've recently added support to speed up Actor migrations by rebooting
the run when it's migrating. This adds docs about that, with code
examples.

The support for this in the Apify SDK is not released yet, it'll go out
in the next SDK release, I'll only merge the docs then.

---------

Co-authored-by: Michał Olender <[email protected]>

Author: fnesveda

sources/platform/actors/development/builds_and_runs/state_persistence.md

@@ -51,7 +51,7 @@ By default, an Actor keeps its state in the server's memory. During a server swi
 
 The [Apify SDKs](/sdk) handle state persistence automatically.
 
-This is done  using the `Actor.on()` method and the `migrating` event.
+This is done using the `Actor.on()` method and the `migrating` event.
 
 - The `migrating` event is triggered just before a migration occurs, allowing you to save your state.
 - To retrieve previously saved state, you can use the [`Actor.getValue`](/sdk/js/reference/class/Actor#getValue)/[`Actor.get_value`](/sdk/python/reference/class/Actor#get_value) methods.
@@ -81,15 +81,15 @@ await Actor.exit();
 <TabItem value="Python" label="Python">
 
 ```python
-from apify import Actor
+from apify import Actor, Event
 
-async def actor_migrate():
+async def actor_migrate(_event_data):
     await Actor.set_value('my-crawling-state', {'foo': 'bar'})
 
 async def main():
     async with Actor:
         # ...
-        Actor.on('migrating', actor_migrate)
+        Actor.on(Event.MIGRATING, actor_migrate)
         # ...
 ```
 
@@ -128,3 +128,50 @@ async def main():
 </Tabs>
 
 For improved Actor performance consider [caching repeated page data](/academy/expert-scraping-with-apify/saving-useful-stats).
+
+## Speeding up migrations
+
+Once your Actor receives the `migrating` event, the Apify platform will shut it down and restart it on a new server within one minute.
+To speed this process up, once you have persisted the Actor state,
+you can manually reboot the Actor in the `migrating` event handler using the `Actor.reboot()` method
+available in the [Apify SDK for JavaScript](/sdk/js/reference/class/Actor#reboot) or [Apify SDK for Python](/sdk/python/reference/class/Actor#reboot).
+
+<Tabs groupId="main">
+<TabItem value="JavaScript" label="JavaScript">
+
+```js
+import { Actor } from 'apify';
+
+await Actor.init();
+// ...
+Actor.on('migrating', async () => {
+    // ...
+    // save state
+    // ...
+    await Actor.reboot();
+});
+// ...
+await Actor.exit();
+```
+
+</TabItem>
+<TabItem value="Python" label="Python">
+
+```python
+from apify import Actor, Event
+
+async def actor_migrate(_event_data):
+    # ...
+    # save state
+    # ...
+    await Actor.reboot()
+
+async def main():
+    async with Actor:
+        # ...
+        Actor.on(Event.MIGRATING, actor_migrate)
+        # ...
+```
+
+</TabItem>
+</Tabs>