Apply naming scheme to btrfs snapshot instead of its topfolder

[zilexa]

Currently, Timeshift for BTRFS stores its snapshots like this:

timeshift-btrfs/snapshots/2022-06-21_11-15-26/@
ID 1536 gen 203902 top level 5 path timeshift-btrfs/snapshots/2022-06-21_11-15-26/@home
ID 1537 gen 207196 top level 5 path timeshift-btrfs/snapshots/2022-06-21_11-17-54/@
ID 1538 gen 203911 top level 5 path timeshift-btrfs/snapshots/2022-06-21_11-17-54/@home

The snapshots all have the same name but reside in separate timestamped folder. This makes it difficult to automate backing up snapshots (btrfs send|receive) to other locations.
Instead, I would like to suggest the following:

timeshift-btrfs/snapshots/2022-06-21_11-15-26/@
ID 1536 gen 203902 top level 5 path timeshift-btrfs/snapshots/@home_2022-06-21_11-15-26
ID 1538 gen 203911 top level 5 path timeshift-btrfs/snapshots/@home_2022-06-22_11-12-59
ID 1537 gen 207196 top level 5 path timeshift-btrfs/snapshots/@_2022-06-21_11-17-54
ID 1537 gen 207196 top level 5 path timeshift-btrfs/snapshots/@_2022-06-22_11-12-41

Storing all snapshots in 1 folder (or @ and @home in seperate folders) instead of having a root (timestamped) folder for each snapshot.

This way tools like btrbk can easily be used to find all snapshots and move them daily to backup targets, locally and remote or even via USB.