Add container labels field from ECS

Signed-off-by: ChrsMark <chrismarkou92@gmail.com>

semantic_conventions/resource/container.yaml

@@ -32,3 +32,8 @@ groups:
         brief: >
           Container image tag.
         examples: ['0.1']
+      - id: labels.<key>
+        type: string
+        brief: >
+          Container labels, `<key>` being the label name, the value being the label value.
+        examples: [ 'container.labels.app=nginx']

specification/resource/semantic_conventions/container.md

@@ -7,13 +7,14 @@
 **Description:** A container instance.
 
 <!-- semconv container -->
-| Attribute  | Type | Description  | Examples  | Requirement Level |
-|---|---|---|---|---|
-| `container.name` | string | Container name used by container runtime. | `opentelemetry-autoconf` | Recommended |
-| `container.id` | string | Container ID. Usually a UUID, as for example used to [identify Docker containers](https://docs.docker.com/engine/reference/run/#container-identification). The UUID might be abbreviated. | `a3bf90e006b2` | Recommended |
-| `container.runtime` | string | The container runtime managing this container. | `docker`; `containerd`; `rkt` | Recommended |
-| `container.image.name` | string | Name of the image the container was built on. | `gcr.io/opentelemetry/operator` | Recommended |
-| `container.image.tag` | string | Container image tag. | `0.1` | Recommended |
+| Attribute                | Type | Description | Examples  | Requirement Level |
+|--------------------------|---|--|---|---|
+| `container.name`         | string | Container name used by container runtime. | `opentelemetry-autoconf` | Recommended |
+| `container.id`           | string | Container ID. Usually a UUID, as for example used to [identify Docker containers](https://docs.docker.com/engine/reference/run/#container-identification). The UUID might be abbreviated. | `a3bf90e006b2` | Recommended |
+| `container.runtime`      | string | The container runtime managing this container. | `docker`; `containerd`; `rkt` | Recommended |
+| `container.image.name`   | string | Name of the image the container was built on. | `gcr.io/opentelemetry/operator` | Recommended |
+| `container.image.tag`    | string | Container image tag. | `0.1` | Recommended |
+| `container.labels.<key>` | string | Container labels, `<key>` being the label name, the value being the label value. | `container.labels.app=nginx` | Recommended |
 <!-- endsemconv -->
 
 [DocumentStatus]: https://github.com/open-telemetry/opentelemetry-specification/blob/v1.21.0/specification/document-status.md