Draft: Clean up Helmholtz ID related docs
Helmholtz ID related documentation meanwhile contains some outdated, duplicated and mixed-level information (mixing how-to, conceptual info, etc).
After fixing the principal overall structure via !646 (merged) , the Helmholtz ID related docs should be cleaned up and most relevant issues resolved.
- Review link t.b.a.
- Edit link(s) t.b.d.
Edited by Uwe Jandt (DESY, HIFIS)