Replace lz4 with zstd

In preparation for an upcoming change in the 'tabacco' service to
switch to zstd, make sure the package is available.

roles/float-base/tasks/apt.yml

@@ -112,7 +112,7 @@
       - restic
       - runcron
       - acpid
-      - lz4
+      - zstd
       - man-db
       - jq
       - gpg

roles/float-infra-log-collector/templates/log-collector.logrotate.j2

@@ -3,9 +3,9 @@
 	missingok
 	rotate {{ log_collector_retention_days|default(15) }}
 	compress
-	compresscmd /usr/bin/lz4c
-	compressoptions -z
-	compressext .lz4
+	compresscmd /usr/bin/zstd
+	compressoptions -9
+	compressext .zstd
 	notifempty
 	create 0600 docker-log-collector adm
 	sharedscripts