Add User Agent OS attributes

[rogercoll]

Area(s)

area:os, area:user-agent

Is your change request related to a problem? Please describe.

The current user-Agent attributes don't make any reference to the represented OS. We propose adding semantic convention attributes specifically aimed at extracting the operating system (OS) from user-agent strings. The OS information is already available in the current user_agent.original attribute, but it is embedded within a larger string, making it difficult to reliably extract and utilize. By introducing dedicated semantic convention attributes such as user_agent.os.name, user_agent.os.version, and user_agent.os.family, we can isolate this information for easier parsing and processing.

Describe the solution you'd like

Embed OS attribute under the user_agent namespace: https://github.com/open-telemetry/semantic-conventions/blob/main/docs/attributes-registry/os.md

A similar solution is the Elastic ECS reuse fields: https://www.elastic.co/guide/en/ecs/current/ecs-user_agent.html#_field_reuse_30

Describe alternatives you've considered

No response

Additional context

No response