Link Kubernetes integration page in Cluster page for easy access

Note

This issue has the goal to track what happened in the first iteration of https://gitlab.com/gitlab-org/gitlab-ce/issues/35616, so please refer to that for all the design/discussions. That issue is now focused on the second iteration (since already contains all the relevant information).

Description

In CI/CD > Cluster page we can create a new GKE cluster, and use it for our deployments. It is strictly related to the Kubernetes service integration (Settings > Integrations > Kubernetes), and technically when we create a new GKE cluster the integration is automatically filled with proper data and activated.

We want to deprecate the Kubernetes service integration page, and move it into the Cluster page (https://gitlab.com/gitlab-org/gitlab-ce/issues/35616), and eventually remove the old one (https://gitlab.com/gitlab-org/gitlab-ce/issues/39217).

Before this can be done, we can just create a link in the CI/CD > Cluster page that allows easy access to Settings > Integrations > Kubernetes page.