Recipe for login only clusters

[johrstrom]

This discourse topic came in today about login clusters, and it reminded me of some other topic that I can't now quickly find.

https://discourse.osc.edu/t/set-multiple-login-nodes-in-clusters/1582

In any case, the original topic wanted a cluster that was just a login node, so it appeared in the "Clusters" drop down menu but you could not actually schedule anything on it.

The advice I gave was to have a cluster configuration like so that doesn't have a v2.job section. Only metadata and login information.

```yaml

v2:
metadata:
title: "Pitzer Login Only"
url: "https://www.osc.edu/supercomputing/computing/pitzer"
hidden: false
login:
host: "pitzer.osc.edu"

The topic currently in discourse (linked above) seems to indicate that they would like specific login hosts to show up in their dropdown menus. I.e., break pitzer into 4 distinct hosts/menu items.

You'd accomplish this by creating a cluster file for each like so:
```yaml
# clusters.d/pitzer_01_login.yml
---
v2:
  metadata:
    title: "Pitzer Login 01"
    url: "https://www.osc.edu/supercomputing/computing/pitzer"
    hidden: false
  login:
    host: "pitzer-login01.hpc.osc.edu"

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