lxc-auto: add optional dnsmasq dep wait on startup

lxc-auto: add optional dnsmasq dep wait on startup

Add opt-in support for waiting for dnsmasq to be fully initialized
before starting LXC containers. This addresses issues where containers
that depend on DNS resolution (e.g., AdGuardHome) start before dnsmasq
has loaded its DHCP lease table, resulting in hostnames not being
resolved to IP addresses.

The feature is controlled by two new optional UCI config options in
/etc/config/lxc-auto whose usage is commented therein.

No new depends are introduced with this change.

Signed-off-by: John Audia <redacted>