main/dnsmasq: add subpackage with dbus support

dnsmasq with dbus support is required for NetworkManager when using
dnsmasq as the dns backend, so this adds a new subpackage to build
dnsmasq with that enabled.

this also uses "provides" to set priority for the packages. using
depends=!$pkgname makes it difficult to move from one to another when
something depends on dnsmasq.
8 jobs for !31213 with dnsmasq in 1 minute and 32 seconds
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