Redis datasource host dropdown is not auto-filled for new hosts

[natoscott]

Data source:
Redis.

Describe the bug
When a long-running Redis dashboard is being displayed, and a new host "arrives" (i.e. we start logging it and indexing it in Redis) since the dashboard was first displayed, the host dropdown does not list that new host (only seems to list those hosts that were known when that dashboard was initially displayed).

To Reproduce
Steps to reproduce the behavior:

1. Go to the 'PCP Redis: Host Overview' dashboard
2. Click on 'host' and observe the list of hosts.
3. Start logging for a new host not listed there.
4. Click on 'host' and observe the list of hosts.

Expected behavior
The new host should be available in the dropdown list.

Versions (please complete the following information):

• Performance Co-Pilot: 6.2.1
• Grafana: 9.2.0
• grafana-pcp: 5.1.1
• Redis (if applicable): 7.2.4