Hi,

Upon using piem for some time, I am getting hundreds of generated
branches in my repos. It gets inconvenient after some time, especially
because the branches are not always clearly distinguishable.

I'd like to add a new customization that adds a custom prefix string to
the generated branch names. That way, I can easily see the branches
generated by piem in the list of branches, nicely grouped when sorting
alphabetically.

The patch is attached.