Provide self-contained schema in YAML format

[mih]

Brought up by @christian-monch

This would solve the loading of external schema components, which may change without proper notice.

[mih]

We are providing the output of gen-yaml for some time now. For example,

https://concepts.datalad.org/s/things/v1.static.yaml

However, that appears to be suboptimal. For example, it contains:

imports:
- ../../src/types/v1
- linkml:types

This is wrong in two ways. First it uses relative paths for imports, and second it imports something to begin with.

Whatever is "imported" also appears to be present in that file already.