feat: introduce useCreateChatClient hook (#1916)

### 🎯 Goal

Introduce `useCreateChatClient` hook which takes care of creation and
initiation of `StreamChat` client.

closes: GetStream/stream-chat-react-issues#19

src/components/Chat/hooks/useCreateChatClient.ts

@@ -0,0 +1,51 @@
+import { useEffect, useState } from 'react';
+
+import {
+  DefaultGenerics,
+  ExtendableGenerics,
+  OwnUserResponse,
+  StreamChat,
+  TokenOrProvider,
+  UserResponse,
+} from 'stream-chat';
+
+/**
+ * React hook to create, connect and return `StreamChat` client.
+ */
+export const useCreateChatClient = <SCG extends ExtendableGenerics = DefaultGenerics>({
+  apiKey,
+  tokenOrProvider,
+  userData,
+}: {
+  apiKey: string;
+  tokenOrProvider: TokenOrProvider;
+  userData: OwnUserResponse<SCG> | UserResponse<SCG>;
+}) => {
+  const [chatClient, setChatClient] = useState<StreamChat<SCG> | null>(null);
+  const [cachedUserData, setCachedUserData] = useState(userData);
+
+  if (userData.id !== cachedUserData.id) {
+    setCachedUserData(userData);
+  }
+
+  useEffect(() => {
+    const client = new StreamChat<SCG>(apiKey);
+    let didUserConnectInterrupt = false;
+
+    const connectionPromise = client.connectUser(cachedUserData, tokenOrProvider).then(() => {
+      if (!didUserConnectInterrupt) setChatClient(client);
+    });
+
+    return () => {
+      didUserConnectInterrupt = true;
+      setChatClient(null);
+      connectionPromise
+        .then(() => client.disconnectUser())
+        .then(() => {
+          console.log(`Connection for user "${cachedUserData.id}" has been closed`);
+        });
+    };
+  }, [apiKey, cachedUserData, tokenOrProvider]);
+
+  return chatClient;
+};

src/components/Chat/index.ts

@@ -1,3 +1,4 @@
 export * from './Chat';
 export * from './hooks/useChat';
 export * from './hooks/useCustomStyles';
+export * from './hooks/useCreateChatClient';