Update templates to use the comment filter

In both `templates/mongodb.conf.j2` and `templates/monogod_init.conf.j2` the top of the file has:
```
# {{ ansible_managed }}
```
This should be changed to:
```
{{ ansible_managed | comment }}
```

The reason for this change is, if `ansible_managed` is multi-lined the comment won't apply to everything, only the first line.