Convert Config classes to public API

These were converted into private classes during the 4.0 migration,
as we were only supporting keyword arguments for the client configuration.

However, that led to a poor user experience, as we had to use `**kwargs`,
instead of listing all the configuration elements in the client constructor.
(IDEs become painfully slow once we list all keyword arguments, as there
are too many of them)

The solution to this problem is to make the Config classes public API
and provide helper methods over them to convert those classes to
dictionaries so that they can be passed in to the client code.

```python

config = Config()
config.cluster_name = "dev2"

client = HazelcastClient(**config.to_dict())

```

We provide full type hints for config elements.

Author: mdumandag

hazelcast/client.py

@@ -4,7 +4,7 @@
 import typing
 
 from hazelcast.cluster import ClusterService, _InternalClusterService
-from hazelcast.config import _Config
+from hazelcast.config import Config
 from hazelcast.connection import ConnectionManager, DefaultAddressProvider
 from hazelcast.core import DistributedObjectEvent, DistributedObjectInfo
 from hazelcast.cp import CPSubsystem, ProxySessionManager
@@ -357,7 +357,7 @@ class SomeClassSerializer(StreamSerializer):
     _CLIENT_ID = AtomicInteger()
 
     def __init__(self, **kwargs):
-        config = _Config.from_dict(kwargs)
+        config = Config.from_dict(kwargs)
         self._config = config
         self._context = _ClientContext()
         client_id = HazelcastClient._CLIENT_ID.get_and_increment()