Add DirectoryIndex to fallback for resources

[wimme002]

When DirectoryIndex is set FallbackResource disabled will do nothing because apache falls back to DirectoryIndex.

[Philosoft]

I haven't touched Apache in years but may be Options -Indexes will be more robust? On a VirtualHost level, since nowadays directory index is veeery rarely used feature.

Docs: https://httpd.apache.org/docs/2.4/mod/core.html#options

[javiereguiluz]

Thanks for this proposal and the review! We finally merged it because, as you said, the Options directive should be defined at VirtualHost level ... so better only change the config of this <Directory> of resources.