Moving the scripts to a common directory not only vastly simplifies the
zzz-gluon-upgrade script, but also allows to define an ordering of such
scripts across packages.

"gluon-node-info": add section system and option role; add announce script to announce the role as nodeinfo;
add invariant script "001-node-system" to add section "system" if not exist; add invariant script "010-node-role"
to add section "system" if not exist; add invariant script "010-node-role" to set role to default value
(site.roles.default) if not exist; depends on new site.conf section

All announce.d scripts have been moved to /lib/gluon/announce/announce.d
The script /lib/gluon/announce/announce.lua will collect all information
and output json.

This also fixes the type of a few fields which were strings instead of numbers.