Revisit categorization of formdata nodes

The HCM demo's bootstrap overrides still contain a TODO to categorize children of /formdata as runtime. Searching through the code, I see that some demo projects bootstrap a 2-level formdata skeleton (26 times 26 hst:formdatacontainer nodes), as configuration. (replication demo, content blocks demo), while HST already provides this.

My hunch is that HST should define /formdata as config, with its (residual) child node types being of type runtime. They're probably auto-created by HST (or they should be? to be confirmed.), so all these 1400-line YAML files can be thrown out.

I created a separate issue for this, to be able to close the parent issue (HCM-123) working towards 12.0 Beta.