Update network connection fields

[axw]

Motivation/summary

The OTel semantic conventions for network connection type have evolved: net.host.connection_type is now net.host.connection.type and net.host.connection.subtype. See open-telemetry/opentelemetry-specification#1759. This PR extends #5436 to adapt to these changes.

Support Elastic APM agents sending "network.connection.type" ("n.c.t" in RUMv3) in metadata, which will be added to all events in the stream. This is currently intended for RUM. In the future we may want to support setting this at the even level too, to cater for operation-specific network information.

Finally, the Elasticsearch field names have been changed to network.connection.type and network.connection.subtype.

Checklist

• Update CHANGELOG.asciidoc
  - [ ] Documentation has been updated

How to test these changes

1. Run the iOS agent
2. Check that the network.connection.type and network.connection.subtype fields are recorded

Related issues

#5203

[apmmachine]

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• Start Time: 2021-08-04T07:48:52.157+0000

• Duration: 41 min 37 sec

• Commit: 94fe9fd

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Total	5948

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[simitt]

What is the urgency of this PR being backported to 7.14? Does the iOS agent not work with the current fields, or would the network.connection* fields just be ignored?

[bryce-b]

@simitt I mentioned to Andrew in slack: we don't need to backport this to 7.14; I've been holding off on updating the agent with these spec changes due to the Otel spec change not being merged yet.

[mergify]

This pull request is now in conflicts. Could you fix it @axw? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b network-connection-subtype upstream/network-connection-subtype
git merge upstream/master
git push upstream network-connection-subtype

[mergify]

This pull request is now in conflicts. Could you fix it @axw? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b network-connection-subtype upstream/network-connection-subtype
git merge upstream/master
git push upstream network-connection-subtype

[simitt]

Cannot yet be tested as the latest version of the iOS agent does not contain the change; it still sends net.host.connection_type instead of net.host.connection.type, see https://github.com/elastic/apm-agent-ios/blob/main/Sources/Instrumentation/NetworkInfo/NetworkStatusInjector.swift#L28.

@bryce-b any update on when this will be changed in the agent?

[bryce-b]

@Silvia These changes will be in this week.