Prometheus exporter: Add unit to metric names, and convert unit to words

[dashpole]

From the OTel prometheus compatibility spec:

The Unit of an OTLP metric point MUST be added as OpenMetrics UNIT metadata. Additionally, the unit MUST be added as a suffix to the metric name, and SHOULD be converted to base units recommended by OpenMetrics when possible. The unit suffix comes before any type-specific suffixes.

For now, I would hold off trying to convert to base units (e.g. milliseconds to seconds), but would still encourage converting from abbreviations to full words for the unit (e.g. ms to milliseconds).

For example, a metric with name "foo", type=monotonic sum, unit=ms should have the name: foo_milliseconds_total.

[github-actions]

This issue is stale because it has been open 60 days with no activity. Remove stale label or comment or this will be closed in 14 days.

[dashpole]

The updated specification now states:

The Unit of an OTLP metric point SHOULD be converted to the equivalent unit in Prometheus when possible. This includes:

• Converting from abbreviations to full words (e.g. "ms" to "milliseconds").
• Dropping the portions of the Unit within brackets (e.g. {packets}). Brackets MUST NOT be included in the resulting unit. A "count of foo" is considered unitless in Prometheus.
• Special case: Converting "1" to "ratio".
• Converting "foo/bar" to "foo_per_bar".

The resulting unit SHOULD be added to the metric as OpenMetrics UNIT metadata and as a suffix to the metric name unless the metric name already contains the unit, or the unit MUST be omitted. The unit suffix comes before any type-specific suffixes.

Hopefully this helps clarify the expected behavior.

[github-actions]

This issue is stale because it has been open 60 days with no activity. Remove stale label or comment or this will be closed in 14 days.

[github-actions]

This issue was closed because it has been stale for 14 days with no activity.

[dashpole]

This is still relevant. I would appreciate it if this was reopened.