fix: respect ctx in cmds run in DialContext (#620)

Update DialContext() to use the new DoContext() methods (added in v1.8.6)
when configuring auth/clientName/db during connection creation.

This prevents DialContex() from blocking for a long time if the redis server is
unresponsive.

redis/conn.go

@@ -291,21 +291,21 @@ func DialContext(ctx context.Context, network, address string, options ...DialOp
 			authArgs = append(authArgs, do.username)
 		}
 		authArgs = append(authArgs, do.password)
-		if _, err := c.Do("AUTH", authArgs...); err != nil {
+		if _, err := c.DoContext(ctx, "AUTH", authArgs...); err != nil {
 			netConn.Close()
 			return nil, err
 		}
 	}
 
 	if do.clientName != "" {
-		if _, err := c.Do("CLIENT", "SETNAME", do.clientName); err != nil {
+		if _, err := c.DoContext(ctx, "CLIENT", "SETNAME", do.clientName); err != nil {
 			netConn.Close()
 			return nil, err
 		}
 	}
 
 	if do.db != 0 {
-		if _, err := c.Do("SELECT", do.db); err != nil {
+		if _, err := c.DoContext(ctx, "SELECT", do.db); err != nil {
 			netConn.Close()
 			return nil, err
 		}