Backup and restore process (#641)

* Make db dump more modular

* Add basic backup and restore scripts

* Exit on error

* Exit with error code in case of missing file

* Determine volumes location programatically

A bit hacky, maybe there's a better way - open for suggestions!

* gzip database dump

* Restore database

* Fail on pipe errors

* Encrypt backup using gpg; improve log messages

* Ensure database container is up during dump and import

* Restore volumes

helpers.sh

@@ -175,11 +175,7 @@ btcpay_restart() {
 btcpay_dump_db() {
     pushd . > /dev/null
     cd "$(dirname "$BTCPAY_ENV_FILE")"
-    backup_dir="/var/lib/docker/volumes/backup_datadir/_data"
-    if [ ! -d "$backup_dir" ]; then
-        docker volume create backup_datadir
-    fi
-    local filename=${1:-"postgres-$(date "+%Y%m%d-%H%M%S").sql"}
-    docker exec $(docker ps -a -q -f "name=postgres_1") pg_dumpall -c -U postgres > "$backup_dir/$filename"
+    local file_path=${1:-"postgres-$(date "+%Y%m%d-%H%M%S").sql.gz"}
+    docker exec $(docker ps -a -q -f "name=postgres_1") pg_dumpall -c -U postgres | gzip > "$file_path"
     popd > /dev/null
 }