Problem/motivation
In #1866610: Introduce Kwalify-inspired schema format for configuration the schema files were merged into one big file per module/theme on suggestion from @effulgentsia & moved into the regular config directory. Practical application of this (eg. with Views at #1910606: Complete configurations schema for Views) proved ineffective and the need to move it out of the regular config directory came up as well as the possibility to split schema files into more logical units as needed.
Proposal
- Modify schema discovery to look for schema files under a subdirectory in config directories called 'schema'.
- Move all existing files there.
- Make schema discovery code find all schema files in that directory not just one.
