[FRE] Support for custom "summary" field

I'd like to be able to set my custom string as session "summary". The rationale is that I can i.e. put ticket number there or anything meaningful for me which would me then help easily navigate thru existing sessions which is pretty hard right now as current summary is often not clear and it's also limited in length.
Custom summary could but starting argument (like --summary) and if given, It should never be rewritten.