log: add file handler for ogLive "real time log"

Clients running in ogLive can show log messages via a lighttp server.
Particularly, a html page named "real time log" consists of <text-area>
tags with the contents of two particular text files
/tmp/session.log and /tmp/command.log

Adds a Python logging handler in order to write ogClient log messages
into /tmp/session.log. This way ogClient logs are show in the "real time
log" html page too.

src/log.py

@@ -58,8 +58,17 @@ def _default_logging_live():
                 'filename': f'/opt/opengnsys/log/{getifaddr(os.getenv("DEVICE"))}.log',
             }
         }
+    rtlog = {
+            'rtlog': {
+                'class': 'logging.FileHandler',
+                'formatter': 'formatter.syslogtime',
+                'filename': f'/tmp/session.log',
+            }
+        }
     logconfig['handlers'].update(samba)
+    logconfig['handlers'].update(rtlog)
     logconfig['loggers']['']['handlers'].append('samba')
+    logconfig['loggers']['']['handlers'].append('rtlog')
     return logconfig