MM-23935 extend session expiry on user activity (#14275)

* MM-23935  extend session expiry on user activity

- if user types anything before a session expires the session will be extended to now + session length

- ensures new session expiries are not written to DB too frequently

- new session store func for updating session ExpiresAt

- session length defaults for mobile and web/ldap changed from 180 days to 30 days

wsapi/user.go

@@ -13,6 +13,8 @@ func (api *API) InitUser() {
 }
 
 func (api *API) userTyping(req *model.WebSocketRequest) (map[string]interface{}, *model.AppError) {
+	api.App.ExtendSessionExpiryIfNeeded(&req.Session)
+
 	if api.App.Srv().Busy.IsBusy() {
 		// this is considered a non-critical service and will be disabled when server busy.
 		return nil, NewServerBusyWebSocketError(req.Action)