Add Geo fields from Elastic Common Schema

[AlexanderWert]

What are you trying to achieve?

Some observability use cases require localization of resources. Examples are:

• Observability of mobile devices: Geographically localizing the mobile devices provides valuable insights into how mobile apps perform depending on their location.
• For applications that are geographically distributed across multiple regions and data centers, the geo location can provide useful insights as well.

Having an additional geo namespace on the resource attributes serves use cases as outlined above and allows to filter and group data by geo locations.

As part of the OTEP to support the Elastic Common Schema (ECS), we propose to start with adopting the rich set of the ECS geo fields as a new namespace in the resource attributes.

Additional context.

This is related to this OTEP: open-telemetry/oteps#199

See attached Draft PR for detailed proposal / context: open-telemetry/opentelemetry-specification#2835

[scheler]

1. For mobile devices, the geo attributes will be changing as the user moves around and they cannot be updated on the Resource currently. This PR will have to wait until Ephemeral Resource Attributes oteps#208 is resolved or there's another mechanism introduced that allows changing attributes on a Resource.
2. For apps running in data centers, I believe the customers will have to run a Geo mapping service to map the IP to the geo coordinates. If for some reason this service is unavailable, there should be a way to pass the original source IP in the Resource so that the telemetry backends can use that for the geo mapping. Can you include support for that in this PR or add a reference to it if it's already there?

[rbailey7210]

Please hold until OTEP to merge.

[martinkuba]

Mentioned here
https://github.com/open-telemetry/oteps/blob/main/text/0199-support-elastic-common-schema-in-opentelemetry.md#scope-and-overlap-of-ecs-and-otel-semconv

Related to
#351

[danielgblanco]

@trask I don't have permissions to move this issue to the https://github.com/open-telemetry/semantic-conventions repo. Could you move it?

[danielgblanco]

I've added the triage:rejected:declined label for the spec repo, but I'm leaving the issue open until moved to the semconv repo.