fix: [rsync-backup] prevent strict host checking

This security measure is inappropriate here as it will make all client
refuse to backup whenever a new docker image is rebuild.

Signed-off-by: Valentin Lab <valentin.lab@kalysto.org>

rsync-backup/resources/bin/mirror-dir

@@ -77,7 +77,7 @@ mirror-dir:run() {
     mkdir -p "$state_dir"
     rsync_options=(
         ${RSYNC_OPTIONS:-} --stats --out-format='%i %o %f %l %b')
-    ssh_options=(${SSH_OPTIONS:-})
+    ssh_options=(${SSH_OPTIONS:--o StrictHostKeyChecking=no})
 
     for dest in "${dests[@]}"; do
         dest_rsync_options=("${rsync_options[@]}")