Rename system.memory.shared to system.memory.linux.shared

[osullivandonal]

Fixes #3260

Changes

This aligns the shared memory metric with other Linux-specific memory metrics (system.memory.linux.available and system.memory.linux.slab.usage)

There is an open PR in collector-contrib in hostmetricsreceiver (see here) to add the system metric system.memory.shared, and since this is a Linux specific metric, the feedback has been to update the semconv to align with other Linux specific metrics.

Since this semconv has not been implemented yet, it was decided to not mark system.memory.shared as deprecated.

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• CONTRIBUTING.md guidelines followed.
• Change log entry added, according to the guidelines in When to add a changelog entry.
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[ChrsMark]

Looks good based on the relevant guidance: https://github.com/open-telemetry/semantic-conventions/blob/main/docs/non-normative/groups/system/design-philosophy.md#operating-system-in-names

Left one comment about the deprecation of the replaced metric.

[kamphaus]

This PR aligns with the PR discussion: open-telemetry/opentelemetry-collector-contrib#45194 (comment)
and what braydonk proposes in

• [chore] System Semconv OS-exclusive instrumentation philosophy #3261

Should we wait for #3261 to be merged or can this PR proceed already?

[osullivandonal]

This PR aligns with the PR discussion: open-telemetry/opentelemetry-collector-contrib#45194 (comment) and what braydonk proposes in

• [chore] System Semconv OS-exclusive instrumentation philosophy #3261

Should we wait for #3261 to be merged or can this PR proceed already?

There are already semconv for other linux specific metrics under system.memory.linux.* at model/system/metrics.yaml such as:

• system.memory.linux.available
• system.memory.linux.slab.usage

Given that do we need to wait for #3261 ?