Backup pocket-id database

[stackptr]

Resolves #246

[stackptr]

Some notes on how to do a restore:

# Download latest snapshot from R2:
sudo env $(sudo cat /run/agenix/restic-env | xargs) \
  restic -r s3:https://9c12166db465350c0f02410b390d0cbc.r2.cloudflarestorage.com/restic \
    --password-file /run/agenix/restic-password \
    restore latest --target /tmp/restore

cd /tmp/restore

# Validate that the snapshot has expected contents
zcat var/backup/postgresql/pocketid.sql.gz | less

# Restore via psql
psql -U postgres -d pocket_id < var/backup/postgresql/pocketid.sql.gz

Loading the env for restic is a little tedious, it could be easier to do this as root instead of via sudo.

I didn't try this out because the snapshot looks sensible enough. However, I'll probably try restoring snapshot 84e4c949 from that bucket when I want to re-enable mastodon.