Deleting "manual events" timeline can render whole sketch inaccessible

**Describe the bug**
When the "manual events" timeline is deleted from a sketch and someone tries to add a new manual event via the UI, the web server crashes with the following error, rendering the whole sketch inaccessible.

```
[2023-07-10 09:48:40 +0000] [145] [DEBUG] GET /api/v1/sketches/3/
[2023-07-10 09:48:40,818] timesketch.opensearch/ERROR Unable to count indices (index not found)
[2023-07-10 09:48:40 +0000] [145] [ERROR] Error handling request /api/v1/sketches/3/
Traceback (most recent call last):
File "/usr/local/lib/python3.10/dist-packages/gunicorn/workers/sync.py", line 135, in handle
self.handle_request(listener, req, client, addr)
File "/usr/local/lib/python3.10/dist-packages/gunicorn/workers/sync.py", line 176, in handle_request
respiter = self.wsgi(environ, resp.start_response)
File "/usr/local/lib/python3.10/dist-packages/flask/app.py", line 2213, in __call__
return self.wsgi_app(environ, start_response)
File "/usr/local/lib/python3.10/dist-packages/flask/app.py", line 2193, in wsgi_app
response = self.handle_exception(e)
File "/usr/local/lib/python3.10/dist-packages/flask_restful/__init__.py", line 298, in error_router
return original_handler(e)
File "/usr/local/lib/python3.10/dist-packages/flask/app.py", line 2190, in wsgi_app
response = self.full_dispatch_request()
File "/usr/local/lib/python3.10/dist-packages/flask/app.py", line 1486, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/usr/local/lib/python3.10/dist-packages/flask_restful/__init__.py", line 298, in error_router
return original_handler(e)
File "/usr/local/lib/python3.10/dist-packages/flask/app.py", line 1484, in full_dispatch_request
rv = self.dispatch_request()
File "/usr/local/lib/python3.10/dist-packages/flask/app.py", line 1469, in dispatch_request
return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args)
File "/usr/local/lib/python3.10/dist-packages/flask_restful/__init__.py", line 489, in wrapper
resp = resource(*args, **kwargs)
File "/usr/local/lib/python3.10/dist-packages/flask/views.py", line 109, in view
return current_app.ensure_sync(self.dispatch_request)(**kwargs)
File "/usr/local/lib/python3.10/dist-packages/flask_restful/__init__.py", line 604, in dispatch_request
resp = meth(*args, **kwargs)
File "/usr/local/lib/python3.10/dist-packages/flask_login/utils.py", line 290, in decorated_view
return current_app.ensure_sync(func)(*args, **kwargs)
File "/usr/local/src/timesketch/timesketch/api/v1/resources/sketch.py", line 393, in get
count_agg = self.datastore.client.search(
File "/usr/local/lib/python3.10/dist-packages/opensearchpy/client/utils.py", line 177, in _wrapped
return func(*args, params=params, headers=headers, **kwargs)
File "/usr/local/lib/python3.10/dist-packages/opensearchpy/client/__init__.py", line 1593, in search
return self.transport.perform_request(
File "/usr/local/lib/python3.10/dist-packages/opensearchpy/transport.py", line 412, in perform_request
raise e
File "/usr/local/lib/python3.10/dist-packages/opensearchpy/transport.py", line 373, in perform_request
status, headers_response, data = connection.perform_request(
File "/usr/local/lib/python3.10/dist-packages/opensearchpy/connection/http_urllib3.py", line 282, in perform_request
self._raise_error(response.status, raw_data)
File "/usr/local/lib/python3.10/dist-packages/opensearchpy/connection/base.py", line 330, in _raise_error
raise HTTP_EXCEPTIONS.get(status_code, TransportError)(
opensearchpy.exceptions.RequestError: RequestError(400, 'index_closed_exception', 'closed')
```

**To Reproduce**
Steps to reproduce the behavior:
1. In a test sketch, add a manual event using the "Add Manual Event" button.
2. Reload the page to get the "Manual events" timeline.
3. Delete the "Manual events" timeline via the UI by clicking on the three dot menu and then Delete.
4. Reload the page and the sketch will return a Server Side error notice and only show the "It's empty around here" page.

**Expected behavior**
It should create a new "Manual events" timeline if the first one was deleted.

Start in timesketch/api/v1/resources/sketch.py around the get method at line 393, then reproduce the issue by deleting the Manual events timeline and reloading the sketch. Trace the datastore search when the timeline or index is absent or closed. Done means reloading does not crash and adding a manual event creates a new Manual events timeline.

Written by the indexing model from the issue text.