Just to add on to lyndidon response, there is not such command syntax such as port role = L2Uplink. To create such a design you set the interface port-mode to trunk, and then make the interface a member of which VLANs you want to communicate on this trunk (802.1q tagged) interface. You can also use key word "all" to place all created VLANs as member of this Trunk/Tagged Interface.
Below are some links with information you may find useful:
NOTE: Since your product is an EX2300, this product uses ELS style syntax
https://kb.juniper.net/InfoCenter/index?page=content&id=KB11234