agendaupdate should be able to create new events vs. just updating existing events

[dbarnett]

Would be nice to be able to create new events in batch using a mechanism similar to the agendaupdate command.

Per #550 (comment), it can currently update existing events but is missing:

• A feature to add new events through this interface instead of only updating events with existing IDs

@michaelmhoffman

[michaelmhoffman]

I added an insert action that does this years ago, and it is already released. Unfortunately, I did not edit GitHub issues at the time to make this clear.

How to use:

1. Run gcalcli agenda --tsv with --details action included.
2. Make a new row, leaving id empty, and setting action to insert instead of the patch provided for existing objects.