command line option to use a different config file than timeshift.json #336

Is your feature request related to a problem? Please describe.
I have a huge home folder.
For managing different situations at the moment I start timeshift-gtk and change manually destination or filters to switch between pure backups for linux and backups that include (non-hidden) config files (some blender addons), personal data and virtualbox windows images.
This is tedious and I tend to either

• miss backuping up some data or
• I run the danger of deleting personal data with restoring linux from a snapshot

On the command line there is already the --target-device option which is very useful but there is no way to filter the files. This could only be done by modifying (and later restoring) /etc/timeshift/timeshift.json. For me modifying the existing timeshfit.json is too dangerous as too much could go wrong.

Describe the solution you'd like
I would like to have an option for the command line to select a config file other than the default timeshift.json. With this I could add a line to the existing /etc/cron.d/timeshift-hourly so that cron can take care of different backup strategies. It should be obvious that this second backup must have a separate target device.

Alternatively a command line option to exclude files (as rsync does) would be helpful in combination with the --target-device option.

This possible future /etc/cron.d/timeshift-hourly would be my prefered solution:

# default entry (no config file option = use /etc/timeshift/timeshift.json)
0 * * * * root timeshift --check --scripted
# custom entry
20  * * * * root timeshift --check --scripted --config-file /etc/timeshift/user_config_1.json
# maybe even?
40  * * * * root timeshift --check --scripted --config-file /etc/timeshift/user_config_2.json

Describe alternatives you've considered
At the moment I use rsync in cron for personal data, but I'm not good at scripting, just one line in cron. So I only have one local backup of important personal files. I can't go back to a specific point in time to look up changes I made to some files. Once in a while I create manually other snapshots.
In addition I use lsyncd to mirror the complete timeshift mountpoint to a remote location (Yes, I know, this is likely to miss files, I would not restore the operation system, only personal data from this).