Test-infra: Spyglass doesn't handle Prow jobs

[ibzib]

1. The current deployment of Spyglass doesn't handle Prow jobs (via /view/prowjob/), which is a regression as it did work in some previous iteration. This seems to be because there's no ArtifactFetcher corresponding to Prow jobs.

2. After the /view/prowjob/ endpoint is fixed, the Spyglass link on Deck needs to be updated as well (I mistakenly hard coded it to /view/gcs/).

/cc @paulangton @krzyzacy @BenTheElder

[stevekuznetsov]

/assign @ibzib

[stevekuznetsov]

We should be a little more careful, we don't have any control over when people roll out changes to deck.

[BenTheElder]

We should be careful, but people also should not depend on spyglass yet, which is why it's still behind a "feature gate"

[stevekuznetsov]

Yep, just good habits starting early, all that jazz :)

[spiffxp]

/remove-priority critical-urgent
/priority important-soon
I'd like to try keeping the red priority for things that are breaking/blocking existing workflows