feat: Refresh deployments list every 15s

[maxpatiiuk]

From @grantfitzsimmons:

Everyone– please make sure you refresh your browser tab for the Test Panel every time before deploying or changing any deployments! If you do not, you will likely erase other people's deployments that have been made between the last time you accessed the panel and now. Thank you!

I thought the test panel already refreshed the deployments list every 15s, but I might have misremembered, or this feature broke

[grantfitzsimmons]

15 seconds might not be frequently enough. There's been moments recently where there are eight concurrent users on the system.

[maxpatiiuk]

true.
there are apps with thousands of concurrent users. many of them refresh in realtime using web sockets, so that the content is not stale for long