trace/http: Add http.{request,response}.size attributes

These attributes are the number of bytes in the request or response,
including headers. The names were chosen by taking the [ECS HTTP fields]
and replacing `bytes` with `size`, as for `http.request.content.size`.

closes #38

[ECS HTTP fields]: https://www.elastic.co/guide/en/ecs/current/ecs-http.html

semantic_conventions/trace/http.yaml

@@ -22,6 +22,16 @@ groups:
           is often, but not always, present as the [Content-Length](https://www.rfc-editor.org/rfc/rfc9110.html#field.content-length)
           header. For requests using transport encoding, this should be the compressed size.
         examples: 3495
+      - id: request.size
+        type: int
+        brief: >
+          Total size in bytes of the request (body and headers).
+        examples: 1437
+      - id: response.size
+        type: int
+        brief: >
+          Total size in bytes of the response (body and headers).
+        examples: 1437
       - ref: http.request.method
         sampling_relevant: true
       - ref: network.transport

specification/trace/semantic_conventions/http.md

@@ -92,6 +92,8 @@ sections below.
 | `http.response.status_code` | int | [HTTP response status code](https://tools.ietf.org/html/rfc7231#section-6). | `200` | Conditionally Required: If and only if one was received/sent. |
 | `http.request.body.size` | int | The size of the request payload body in bytes. This is the number of bytes transferred excluding headers and is often, but not always, present as the [Content-Length](https://www.rfc-editor.org/rfc/rfc9110.html#field.content-length) header. For requests using transport encoding, this should be the compressed size. | `3495` | Recommended |
 | `http.response.body.size` | int | The size of the response payload body in bytes. This is the number of bytes transferred excluding headers and is often, but not always, present as the [Content-Length](https://www.rfc-editor.org/rfc/rfc9110.html#field.content-length) header. For requests using transport encoding, this should be the compressed size. | `3495` | Recommended |
+| `http.request.size` | int | Total size in bytes of the request (body and headers). | `1437` | Recommended |
+| `http.response.size` | int | Total size in bytes of the response (body and headers). | `1437` | Recommended |
 | `http.request.method` | string | HTTP request method. | `GET`; `POST`; `HEAD` | Required |
 | [`network.protocol.name`](span-general.md) | string | [OSI Application Layer](https://osi-model.com/application-layer/) or non-OSI equivalent. The value SHOULD be normalized to lowercase. | `http`; `spdy` | Recommended: if not default (`http`). |
 | [`network.protocol.version`](span-general.md) | string | Version of the application layer protocol used. See note below. [1] | `1.0`; `1.1`; `2.0` | Recommended |