Service environment correlation

# Description

Agent implementation of specification change #766

Summary of the required changes:
- updating documentation in https://github.com/elastic/observability-docs/pull/2731 to invite users to provide values for `service.version` and `service.environment` (by using `SERVICE_NAME` and `ENVIRONMENT` configurations respectively).
- when ecs-logging library is used:
- agents provide fallback values if they are not set in ecs-logging configuration for: `service.name`, `service.version` and `service.environment`. Giving priority to existing values (if any) avoids making this a breaking change.
- (optional but highly recommended) if values from agent configuration and ecs-logging configuration differ, issuing a warning is relevant to inform end user that traces and logs can't be properly correlated.
- when log reformatting (and log sending) is used:
- produced ECS logs should contain `service.name`, `service.version` and `service.environment` with values from agent configuration.

## Agent Issues
- [x] https://github.com/elastic/apm-agent-java/issues/3051
- [x] https://github.com/elastic/apm-agent-dotnet/issues/2033
- [x] https://github.com/elastic/apm-agent-nodejs/issues/3195
- [x] https://github.com/elastic/apm-agent-python/issues/1772
- [ ] https://github.com/elastic/apm-agent-go/issues/1401
- [ ] https://github.com/elastic/apm-agent-php/issues/879
- [ ] https://github.com/elastic/apm-agent-ruby/issues/1374