Unfortunately, there currently isn't. This was discussed in another thread (see: LEDE is death hole for consumer - #38 by lleachii). Doing so could cause issues on devices that don't have enough space to upgrade all packages at at once. There's no straightforward way to prevent out-of-space issues on so many different types of devices.
You can perform one step in LuCI, though:
- you can press Update lists from the Software Menu in the Web GUI (this perform the same function as opkg update on the command line)
The command line isn't that scary to run upgrades:
opkg update
opkg list-upgradable
opkg upgrade xxxxx yyyyy zzzzz