re-work the default title line of rendered logs

[trentm]

The current title line pattern is roughly:

[@timestamp] LOG.LEVEL (log.logger/service.name on host.hostname): message

I think the parens section is weak. It comes at least partly from my bunyan experience
For comparison:

typical bunyan:  [@timestamp] LEVEL (name/pid on host): message
typical pino:    [@timestamp] LEVEL (pid on host): message
typical winston: [@timestamp] LEVEL: message

Notes:

• bunyan will always have a name field, which is the equivalent of log.logger in ECS.
• bunyan and pino will typically have pid (ECS equivalent is process.pid)
• What about other languages and loggers.
• service.name will typically only be there with automatic injection from APM agents.

[trentm]

Bunyan will include "src" fields in the title line, I think.

• src fields: log.origin.file.* (note that ecs-logging zap logger emits
  "log.origin"."file.name", which adds a surprise)
  • also colorizing these