Update identifier-types.md

I realised we had not made the metric identifier type obvious.

well-known/identifier-types.md

@@ -26,5 +26,6 @@ Here is the list of subclassed identifiers, their purpose, and the list of well-
 | [icarFeedIdentifierType](../types/icarFeedIdentifierType.json) | Identifier schemes for livestock feeds. | [icarFeedIdentifierType.md](../well-known/icarFeedIdentifierType.md) |
 | [icarLocationIdentifierType](../types/icarLocationIdentifierType.json) | Identifier schemes for herd or farm locations. | [icarLocationIdentifierType.md](../well-known/icarLocationIdentifierType.md) |
 | [icarMedicineIdentifierType](../types/icarMedicineIdentifierType.json) | Identifier schemes for national medicine registration. | [icarMedicineIdentifierType.md](../well-known/icarMedicineIdentifierType.md) |
+| [icarMetricIdenfifierType](../types/icarMetricIdentifierType.json) | Identifier types for statistics and metrics. | [icarMetricIdentifierType.md](../well-known/icarMetricTypeIdentifier.md) |
 | [icarPropertyIdentifierType](../types/icarPropertyIdentifierType.json) | Identification schemes for feed properties. | [icarPropertyIdentifierType.md](../well-known/icarPropertyIdentifierType.md) |
 | [icarTraitLabelIdentifierType](../types/icarTraitLabelIdentifierType.json) | National or industry trait labels. | [icarTraitLabelIdentifierType.md](../well-known/icarTraitLabelIdentifierType.md) |