Improve IPC idle connection management

IPC server determines if a connection is idle or not by checking if the connection does not have any IO activity for a predefined max idle time. An idle connection will be closed even if the connection still has outstanding requests or replies. This causes RPC failures when a server becomes slow or if a request takes a long time to be served. In jira, I'd like to propose the following changes to IPC idle management:
1. Add data structures to the IPC server that keep track of outstanding requests.
2. IPC server does not close a connection that has outstanding requests/replies even when it has no IO activities for a while.
3. The default client-side max idle time should be in several minutes not 1 second.
4. The server-side max idle time should be greater than the client-side max idle time, for example, twice of the client-side max idle time. So server mainly deals with clients that are crashed without closing
its connections.