Add Operator as an install option in the homepage

We have all the different installation methods linked in the homepage, except the newly added Operator. Let's add it.

Instead of creating another tile, I opted to use the existing one where we had the Charts. Since the Charts and the Operator are both used to install GitLab in a Kubernetes cluster, it made sense to put them together.

Brought up in Slack https://gitlab.slack.com/archives/C1FCTU4BE/p1652978822736419

balu: I know we are publishing Operator docs to https://docs.gitlab.com/operator/, but I don't see a link to it at the docs homepage. Should there be one? Or is the intended navigation flow Main page > Charts > Go to "Install with GitLab Operator" on the left sidebar (I don't think it is)?

Mitch Nielsen: I think it'd be good to have a link to that from the homepage, the flow you mentioned above isn't ideal. Unless we're intentionally leaving it out until it hits 1.0?