ECS logging libraries setting the `ecs.version`

When making the ECS logger and formatter libraries GA, most of them will be versioned independently of the stack or ECS, therefore library versions will be starting with `v1.0.0.`

The loggers set the `ecs.version` according to the [ecs-logging spec](https://github.com/elastic/ecs-logging/blob/7fc00daf3da87e749b0053c592eca61a38afc6ce/spec/spec.json#L34-L38). The current behavior for most loggers is to set the `ecs.version` to the minimal supported ECS version supported by this logger. This has the advantage that the logger libraries do not need to be updated and released on every ECS release. It also seems reasonable to use the minimal supported ECS version when querying log data.

@elastic/ecs does setting the `ecs.version` to the minimal supported version sound reasonable from an ECS perspective?