"metric attributes must have namespaces" decision is not documented in the general metrics guidelines

[joaopgrassi]

In #51 (comment) the TC has voted on the matter of "metric attributes must have namespaces" but the actual decision/guidelines never made to the general metric guidelines in https://github.com/open-telemetry/semantic-conventions/blob/main/docs/general/metrics.md

[pyohannes]

It's already present in the general attribute naming guidelines:

This section applies to Resource, Span, Log, and Metric attribute names (also known as the "attribute keys"). [...]

Names SHOULD follow these rules:

• Use namespacing to avoid name clashes.

This seems to be related to open-telemetry/opentelemetry-specification#3746: do we see metric naming guidelines as an extension of the general attribute naming guidelines?

[joaopgrassi]

I feel it is an "extension" and probably everyone would benefit from it being defined in a more clear way. There is says "SHOULD" follow these rules, but AFAIK the attributes MUST have namespaces now after the TC vote.

[jsuereth]

We are currently treating all SHOULD guidance as MUST for our own semconv definitions.