add --private-template=directory option

[nextime]

--private mount a tmpfs over the user home, so, things like browser extensions and configurations are back to the defaults and you cannot pre-configure it easily.

--private=directory, on the other side, make the user home persistent.

--private-template=directory aim to /opt/firejail/templates/usernamebe an alternative, it act like --private mounting a tmpfs over the user home, and then it copy recursively all the files and dirs from a template directory to the created empty user home.

This way you can put, for example, a preconfigured .config/cromium directory let's says in /opt/firejail/templates/username, and then use
firejail --private-template=/opt/firejail/templates/username cromium

NOTE: as the copy from template is done after mounting the tmpfs to mask the user home, the template directory cannot be copied from inside the original user home.

[netblue30]

Merged, thanks for the patch. I used to have this feature a long time ago and scrapped it. I will rename it private-home.