Avoid using "infrastructure" terminology for all cloud (#1530)

* Avoid using "infrastructure" terminology for all cloud

Infrastructure in cloud has a specific connotation for concepts
explained in Infrastructure-as-a-Service (IaaS). Avoid this
termilogy because it's exclusive of some other services/platforms
that is represented by the "cloud" namespace.

Renaming "infrastructure_service" to "service" also due to the new
key length limits we are considering and infrastructure_service is
a lengthy choice.

semantic_conventions/resource/cloud.yaml

@@ -2,7 +2,7 @@ groups:
   - id: cloud
     prefix: cloud
     brief: >
-      A cloud infrastructure (e.g. GCP, Azure, AWS)
+      A cloud environment (e.g. GCP, Azure, AWS)
     attributes:
       - id: provider
         type:
@@ -42,7 +42,7 @@ groups:
         note: >
           Availability zones are called "zones" on Google Cloud.
         examples: ['us-east-1c']
-      - id: infrastructure_service
+      - id: platform
         type:
           allow_custom_values: true
           members:
@@ -92,7 +92,7 @@ groups:
               value: 'gcp_app_engine'
               brief: Google Cloud App Engine (GAE)
         brief: >
-          The cloud infrastructure resource in use.
+          The cloud platform in use.
         note: >
           The prefix of the service SHOULD match the one specified in `cloud.provider`.
         examples: ['aws_ec2', 'azure_vm', 'gcp_compute_engine']

specification/resource/semantic_conventions/cloud.md

@@ -13,7 +13,7 @@
 | `cloud.account.id` | string | The cloud account ID the resource is assigned to. | `111111111111`; `opentelemetry` | No |
 | `cloud.region` | string | The geographical region the resource is running. Refer to your provider's docs to see the available regions, for example [AWS regions](https://aws.amazon.com/about-aws/global-infrastructure/regions_az/), [Azure regions](https://azure.microsoft.com/en-us/global-infrastructure/geographies/), or [Google Cloud regions](https://cloud.google.com/about/locations). | `us-central1`; `us-east-1` | No |
 | `cloud.availability_zone` | string | Cloud regions often have multiple, isolated locations known as zones to increase availability. Availability zone represents the zone where the resource is running. [1] | `us-east-1c` | No |
-| `cloud.infrastructure_service` | string | The cloud infrastructure resource in use. [2] | `aws_ec2`; `azure_vm`; `gcp_compute_engine` | No |
+| `cloud.platform` | string | The cloud platform in use. [2] | `aws_ec2`; `azure_vm`; `gcp_compute_engine` | No |
 
 **[1]:** Availability zones are called "zones" on Google Cloud.
 
@@ -27,7 +27,7 @@
 | `azure` | Microsoft Azure |
 | `gcp` | Google Cloud Platform |
 
-`cloud.infrastructure_service` MUST be one of the following or, if none of the listed values apply, a custom value:
+`cloud.platform` MUST be one of the following or, if none of the listed values apply, a custom value:
 
 | Value  | Description |
 |---|---|