Add HTTP integration GraphQL query

What does this MR do?

Related to #321674 (closed)

Adds a new alertManagementHttpIntegration to fetch information about a single HTTP Integration by ID.

Why there is no alertManagementIntegration query similar to alertManagementHttpIntegration?

Alert Management Integration consists of two kinds: HTTP Integrations and Prometheus integration. The last can only be present in a single copy and I think there is no need to filter it by ID when it's already fetched from the alertManagementIntegrations query.

If we ignore filtering Prometheus integration in alertManagementIntegration, then alertManagementIntegration and alertManagementHttpIntegration will do exactly the same job.

One may argue, in the future, we may have more integration types and alertManagementIntegration is going to allow us to filter any of them by ID. I would suggest getting back to that discussion once we have more integration types.

GraphQL

Query

query Extract($fullPath: ID!, $id: AlertManagementHttpIntegrationID!) {
  project(fullPath: $fullPath) {
    alertManagementHttpIntegration(id: $id) {
      id
      active
      name
      payloadExample
      payloadAttributeMappings {
        fieldName
        label
        type
      }
    }
  }
}

Query variables

{
  "fullPath": "<PROJECT-FULL-PATH>",
  "id": "gid://gitlab/AlertManagement::HttpIntegration/<ID>"
}

Screenshots (strongly suggested)

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