Enhance the visibility of the gNB application state

An operator of a multi-cell network typically analyses syslog events. Each gNB has a unique name assigned either in config file or preferable passed a command line argument:

--gNBs.[0].gNB_name CELL-34

Passing the name as a command line argument is preferable when multiple gNBs can run on the same Linux server, as it allows for easier distinction between processes. It would be very convenient if, upon application start, nr-softmodem sends a syslog event with the specific gNB name.

In the meantime, an operator can determine the start timestamp by checking the creation time of one of the *.log files generated by nr-softmodem. To ensure the creation time is updated with each application launch, we need to delete the specified file at the start of the application.