* Simplify subsystem jobs
This pr simplifies the subsystem jobs interface. Instead of requiring an
extra message that is used to signal that a job should be ended, a job
now ends when the receiver returns `None`. Besides that it changes the
interface to enforce that messages to a job provide a relay parent.
* Drop ToJobTrait
* Remove FromJob
We always convert this message to FromJobCommand anyway.
* drop in tracing to replace log
* add structured logging to trace messages
* add structured logging to debug messages
* add structured logging to info messages
* add structured logging to warn messages
* add structured logging to error messages
* normalize spacing and Display vs Debug
* add instrumentation to the various 'fn run'
* use explicit tracing module throughout
* fix availability distribution test
* don't double-print errors
* remove further redundancy from logs
* fix test errors
* fix more test errors
* remove unused kv_log_macro
* fix unused variable
* add tracing spans to collation generation
* add tracing spans to av-store
* add tracing spans to backing
* add tracing spans to bitfield-signing
* add tracing spans to candidate-selection
* add tracing spans to candidate-validation
* add tracing spans to chain-api
* add tracing spans to provisioner
* add tracing spans to runtime-api
* add tracing spans to availability-distribution
* add tracing spans to bitfield-distribution
* add tracing spans to network-bridge
* add tracing spans to collator-protocol
* add tracing spans to pov-distribution
* add tracing spans to statement-distribution
* add tracing spans to overseer
* cleanup