Use MongoDB setFeatureCompatibilityVersion 4.2 on Snap. TODO: Docker.

Thanks to GuidoDr and xet7 !

Related #3247

snap-src/bin/mongodb-control

@@ -95,6 +95,6 @@ else
 
     # Drop indexes on database upgrade, when starting MongoDB
     #mongo wekan --eval "db.getCollectionNames().forEach(function(col_name) { var coll = db.getCollection(col_name); coll.dropIndexes(); });" $BIND_OPTIONS
-    mongo wekan --eval 'db.adminCommand({ setFeatureCompatibilityVersion: "4.4" });' $BIND_OPTIONS
+    mongo wekan --eval 'db.adminCommand({ setFeatureCompatibilityVersion: "4.2" });' $BIND_OPTIONS
 
 fi