Should `system` metrics be renamed to `os` (for consistency with attributes)?

[lmolkova]

We have os.name, os.version, type, etc attributes, but use system on metrics (system.cpu.time, system.memory.usage, etc).

System metrics are effectively OS metrics:

https://github.com/open-telemetry/semantic-conventions/blob/5eb37f706894718493af7a668971c651acb80812/docs/system/system-metrics.md?plain=1#L14-L15

We should consider renaming system to os (i.e. (os.cpu.time, ...) for the sake of consistency.

Also I'd expect system metrics to be reported with os resource (it's useful to know the OS type when interpreting specific metric), but it's not documented.