Support custom snippets in apache config

[aelkiss]

I would like to be able to include custom snippets for the Apache configuration in the input variables file rather than having to explicitly put all apache configuration in the apache template. This minimizes the number of variables and amount of conditionality required in the apache template.

[aelkiss]

Note: we added an extra snippet:

Header set X-Robots-Tag "noindex"

for arclight-testing.