fix(modules/unifi): only backup the backup directory

`/var/lib/unifi` is almost 1GB. The data directory contains a lot of
files that are changing constantly, which creates a significant amount
of data to backup everyday. Overall if I need to restore a backup for
unifi, I don't care about metrics and other application data, I only
need to restore a backup, which contains the network configuration.

`/var/lib/unifi/data/backup` is smaller:
```
fcuny@tahoe ~> sudo du -sh /var/lib/unifi/data/backup
332M    /var/lib/unifi/data/backup
```

and each backup is about 12MB:
```
fcuny@tahoe ~> sudo ls -ltrh /var/lib/unifi/data/backup/autobackup|tail -2
-rw------- 1 unifi unifi  12M Jun 22 18:15 autobackup_6.5.55_20220623_0115_1655946900001.unf
-rw------- 1 unifi unifi 5.0K Jun 22 18:15 autobackup_meta.json
```

This will reduce the churn in our daily backup significantly.

Change-Id: Ie39ffa9055605298a82ba6731acc34fd4e29309c
Reviewed-on: https://cl.fcuny.net/c/world/+/471
Tested-by: CI
Reviewed-by: Franck Cuny <franck@fcuny.net>

0 files changed, 0 insertions, 0 deletions