feat(nextcloud): Enable modsecurity

This patch enables mod security for nextcloud and sets up the default
exceptions maintained by the CRS maintainers.

References:
https://github.com/coreruleset/coreruleset/blob/554fb063c2613ca9cb470524c721476c2eedf62f/rules/REQUEST-903.9003-NEXTCLOUD-EXCLUSION-RULES.conf