CLI database backup and restore

[Alkarex]

Can also be used to migrate from one database to another (e.g. MySQL to PostgreSQL) or to ease upgrade to a major PostgreSQL version (e.g. 15 to 16).

My use-case is that PostgreSQL does not support easy migration to newer major versions, especially not when using Docker docker-library/postgres#37

Instructions assuming a Docker Compose structure like https://github.com/FreshRSS/FreshRSS/tree/edge/Docker/freshrss but can be adapted to other Compose structures or basic Docker (without Compose).

# Stop FreshRSS container (Web server + cron) during maintenance
docker compose down freshrss

# Optional additional pre-upgrade back-up using PostgreSQL own mechanism
docker compose -f docker-compose-db.yml \
  exec freshrss-db pg_dump -U freshrss freshrss | gzip -9 > freshrss-postgres-backup.sql.gz
# ------↑ Name of your PostgreSQL Docker container
# -----------------------------↑ Name of your PostgreSQL user for FreshRSS
# --------------------------------------↑ Name of your PostgreSQL database for FreshRSS

# Back-up all users respective database to SQLite files
docker compose -f docker-compose.yml -f docker-compose-db.yml run --rm freshrss cli/db-backup.php

# Remove old PostgreSQL container and PostgreSQL data volume
docker compose -f docker-compose-db.yml down --volumes freshrss-db

# Edit your Compose file to use latest postgres:xx
nano docker-compose-db.yml

# Start new PostgreSQL container and new empty PostgreSQL data volume
docker compose -f docker-compose.yml -f docker-compose-db.yml up -d freshrss-db

# Restore all users respective database from SQLite files
docker compose -f docker-compose.yml -f docker-compose-db.yml \
  run --rm freshrss cli/db-restore.php --delete-backup

# Restart a new FreshRSS container after maintenance
docker compose -f docker-compose.yml -f docker-compose-db.yml up -d freshrss

[Alkarex]

* [ ] I lack a mutex

Using the approach of stopping the FreshRSS service instead, during maintenance

[Alkarex]

Fix regression from #6285 for some cases