[Website]: Add GCP to serverless in deployment comparison table

[lon-holden]

Type of issue

None

What documentation page is affected

https://www.elastic.co/docs/deploy-manage/deploy/deployment-comparison

What happened?

We need to add GCP to the Serverless column of the Hosted row under Infra and Cluster management.

Additional info

No response

[leemthompo]

Thanks @lon-holden for flagging, I've opened a PR and the admin docs team will confirm