Option to provide fixed name the output of the backup app

[landmanbester]

Describe the problem that the feature should address
Currently the backup app uses a time stamp to set the default name of the output. This makes it hard to know the name of the output when reusing them (for example as an output of a stimela recipe step). Also, if you are like me and don't use the zarr_dir to reflect the state of the MS when the backup occurred, it's difficult to remember which backup to use to get back to a particular state.

Describe the solution you'd like
It would be useful if one could pass in a fixed name in addition to zarr_dir to provide a more human-proof backup solution. Datetime can still be the default.

Describe alternatives you've considered
I can't see any sane alternatives in the stimela use case above but open to suggestions

[JSKenyon]

This is on my to-do list - I actually want to make it an entirely separate package which QuartiCal simply installs. Part of that change would be to give it a more fully fledged CLI, including something like newpackagename list which can inspect the contents of a directory and print some human readable output. It would also support adding comments to the backups to make this simpler e.g. newpackagename backup -m "Some informative string." otherargs