ref(develop/spans): Clarify span attribute units

Author: Lms24

develop-docs/sdk/telemetry/spans/span-protocol.mdx

@@ -91,6 +91,11 @@ The envelope item payload must contain an `items` array with span one and up to
         "http.response.status_code": {
           "type": "integer",
           "value": 200
+        },
+        "session.duration": {
+          "type": "integer",
+          "value": 164,
+          "unit": "second"
         }
       },
       "links": [
@@ -158,9 +163,9 @@ Attributes are stored as key-value pairs where each value is an object with type
 
 | Property | Type | Required | Description |
 |----------|------|----------|-------------|
-| `type` | string | Yes | The data type of the attribute value. Values: `"string"`, `"integer"`, `"double"`, `"boolean"` |
+| `type` | string | Yes | The data type of the attribute value. Values: `"string"`, `"integer"`, `"double"`, `"boolean", `"string[]"`, `"integer[]"`, `"double[]"`, `"boolean[]"` |
 | `value` | any | Yes | The actual attribute value, must match the specified type |
-| `unit` | string | No | The unit of the attribute value. Example values: `"ms"`, `"s"`, `"bytes"`, `"count"`, `"percent"` |
+| `unit` | string | No | The unit of the attribute value. Example values: `"millisecond"`, `"second"`, `"byte"`, `"ratio"`. Units MUST be one of the [MetricUnit](https://getsentry.github.io/relay/relay_metrics/enum.MetricUnit.html)s supported by Relay, excluding `""`, `"none"` or custom units. |
 
 #### Common Attribute Keys