Add button to install ingress on Kubernetes cluster

Description

Note: General design for applications discussed in https://gitlab.com/gitlab-org/gitlab-ce/issues/38464.

If you have a Kubernetes/GKE cluster defined in CI/CD > Cluster, and want to use Auto DevOps or deploy your web application, you're going to need ingress, ideally with Let's Encrypt. Let's make it easy to configure this by providing a button to install it automatically for you (using Helm).

Proposal

UX should be the one defined in https://gitlab.com/gitlab-org/gitlab-ce/issues/38464.

Links / references

• Part of https://gitlab.com/gitlab-org/gitlab-ce/issues/35956

Documentation blurb

Overview

What is it? Why should someone use this feature? What is the underlying (business) problem? How do you use this feature?

Use cases

Who is this for? Provide one or more use cases.

Feature checklist

Make sure these are completed before closing the issue, with a link to the relevant commit.

• Feature assurance
• Documentation
• Added to features.yml