Merge branch 'zfs-lib-version' into 'master'

fix: specify the Docker image to get the exact version of ZFS libs

# Description
The base Docker image changed the Alpine version: docker-library/docker@a2c3530#diff-6310ae22d38094ab53b1f574cf959396c604cd52baa59375d636ba8bd5b8ac8c that probably contains major changes of ZFS libs.

This MR specifies the Docker image in order to get the exact version of ZFS libs

See merge request postgres-ai/database-lab!253

Author: agneum

Dockerfile.dblab

@@ -1,4 +1,4 @@
-FROM docker:19
+FROM docker:19.03.14
 
 # Install dependencies.
 RUN apk update && apk add --no-cache bash jq

Dockerfile.dblab-server

@@ -25,13 +25,13 @@
 #   --env VERIFICATION_TOKEN=token \
 #   --env MOUNT_DIR=/var/lib/dblab/clones \
 #   --env UNIX_SOCKET_DIR=/var/lib/dblab/sockets \
-#   --env DOCKER_IMAGE=postgres:12-alpine \
+#   --env DOCKER_IMAGE=postgres:13-alpine \
 #   --detach \
 #   postgresai/dblab-server:latest
 
-FROM docker:19
+FROM docker:19.03.14
 
-# Install dependecies.
+# Install dependencies.
 RUN apk update && apk add --no-cache zfs lvm2 bash util-linux
 
 WORKDIR /home/dblab