Tutorials: updates for NR SA Tutorials

• Update links for the latest Ubuntu 24.04.2 LTS iso file

• Update docker install to the latest instructions on the official website

• Update UHD to v4.8.0.0

• Add support for 'default'/"empty" DNN to CN5G configuration file

  • Add support for 'default' DNN to CN5G configuration file (that will also be used when DNN is not available, "empty" DNN). This configuration will allow most of the COTS UE to get PDUSession without any APN configuration made by the user

  • The 'default'/"empty" DNN configuration support was added in oai/cn5g/oai-cn5g-amf!343 (merged)