I found example at Thorntail Documentation v2.0.0, but I think Thorntail will have more setting items, actually.
Where are specifications of project-defaults.yml
file?
These are not Thorntail-core's setting, but fraction's one. Thus you should refer each faraction's doc.
For example, Datasource setting items are defined at Datasources fraction.
There are items swarm.datasources.data-sources.KEY.allocation-retry
and so on.