Add Hashicorp Vault to the www-gitlab-com images

What does this MR do and why?

This installs Hashicorp Vault in the www-gitlab-com CI images, which is needed for retrieving GCP credentials from https://vault.gitlab.net/

Part of Update scripts/deploy to pull GCP credentials f... (gitlab-com/www-gitlab-com#34143)

Checklist

• (If applicable) Add patches if required for upgrading Ruby version in https://gitlab.com/gitlab-org/gitlab-build-images/-/tree/master/patches/ruby.