Add conf_maxmemory_policy to debian template

Not sure why this isn't in the debian template. Doing a diff on the two templates it appears as if there are a huge number of differences, with the biggest one, for flexibility's sake, being `conf_include` in the rhel edition but not the debian one.

As an outsider of the module, why is it that these two templates are so different? If they are both running redis, I assume that the configuration options are the same no matter the platform redis is running on.