Support Redis Cluster

### Environment

self-hosted (https://develop.sentry.dev/self-hosted/)

### Version

21.7.0

### Steps to Reproduce

use redis cluster

### Expected Result

work normally

### Actual Result

```
Traceback (most recent call last):
File "/usr/local/lib/python3.6/site-packages/celery/app/trace.py", line 412, in trace_task
R = retval = fun(*args, **kwargs)
File "/usr/local/lib/python3.6/site-packages/celery/app/trace.py", line 704, in __protected_call__
return self.run(*args, **kwargs)
File "/usr/local/lib/python3.6/site-packages/sentry_sdk/integrations/celery.py", line 197, in _inner
reraise(*exc_info)
File "/usr/local/lib/python3.6/site-packages/sentry_sdk/_compat.py", line 54, in reraise
raise value
File "/usr/local/lib/python3.6/site-packages/sentry_sdk/integrations/celery.py", line 192, in _inner
return f(*args, **kwargs)
File "/usr/local/lib/python3.6/site-packages/sentry/tasks/base.py", line 46, in _wrapped
result = func(*args, **kwargs)
File "/usr/local/lib/python3.6/site-packages/sentry/tasks/store.py", line 851, in save_event
_do_save_event(cache_key, data, start_time, event_id, project_id, **kwargs)
File "/usr/local/lib/python3.6/site-packages/sentry/tasks/store.py", line 765, in _do_save_event
project_id, assume_normalized=True, start_time=start_time, cache_key=cache_key
File "/usr/local/lib/python3.6/site-packages/sentry/utils/metrics.py", line 192, in inner
return f(*args, **kwargs)
File "/usr/local/lib/python3.6/site-packages/sentry/event_manager.py", line 426, in save
**kwargs,
File "/usr/local/lib/python3.6/site-packages/sentry/event_manager.py", line 1147, in _save_aggregate
group=group, event=event, data=kwargs, release=release
File "/usr/local/lib/python3.6/site-packages/sentry/event_manager.py", line 1327, in _process_existing_aggregate
buffer.incr(Group, update_kwargs, {"id": group.id}, extra)
File "/usr/local/lib/python3.6/site-packages/sentry/utils/services.py", line 102, in
context[key] = (lambda f: lambda *a, **k: getattr(self, f)(*a, **k))(key)
File "/usr/local/lib/python3.6/site-packages/sentry/buffer/redis.py", line 188, in incr
pipe.execute()
File "/usr/local/lib/python3.6/site-packages/redis/client.py", line 3967, in execute
return execute(conn, stack, raise_on_error)
File "/usr/local/lib/python3.6/site-packages/redis/client.py", line 3860, in _execute_transaction
response = self.parse_response(connection, '_')
File "/usr/local/lib/python3.6/site-packages/redis/client.py", line 3926, in parse_response
self, connection, command_name, **options)
File "/usr/local/lib/python3.6/site-packages/redis/client.py", line 892, in parse_response
response = connection.read_response()
File "/usr/local/lib/python3.6/site-packages/redis/connection.py", line 752, in read_response
raise response
redis.exceptions.ResponseError: CROSSSLOT Keys in request don't hash to the same slot
```