CommandInstrumentation

Observes the handling of each command at one fixed seam: around the whole command pipeline of DefaultCommandHandler (processing, acknowledgement, publication and the PROCESSED report). For tracing, metrics and logging, which used to be command filters (V5).

An instrumentation must not change the outcome: it subscribes to around's handling once and passes its completion or error on. Several instrumentations wrap each other in @Order order, the first outermost.