lte: Add support for DC-GBR, 3GPP Release 18 5QIs and PDCP discard timer

This MR modifies the member QosBearerType_e of the structure LogicalChannelConfigListElement_s to include the DC-GBR resource type, along with the already supported non-GBR and GBR types. Due to this modification, the logic of how the resource type of a flow is considered in the EpsBearer class is changed, and accordingly, the code in various classes that were using the old logic, is modified. Moreover, the EpsBearer class is extended to support 3GPP Release 18 5QIs. Finally, we add support for discarding a packet when passed from the PDCP to the RLC layer, in case that the head-of-line delay exceeds the PDB or a value set by the user. PDCP discarding can be enabled through the EnablePdcpDiscarding attribute.