Define hostname naming convention

we almost agreed to:

• name hostname as <feature>-<subsystem> like bee-b1
• use canonical acronyms for subsystem, like sm1/ics/infra/pfi/mcs, except for [brn][1-4] of xCU
• have one (or two?) digit numerical character at the last in <feature> or <subsystem> for identical multiple instances, like b1/b2/b3/b4

need to be documented in ics_doc.