Adjust blackbox prober additional scrape targets.

[cjwagner]

1. Scraping https://prow.k8s.io/hook results in 405, not 200. (We don't really need to scrape /hook anyways since the hook service is already monitored for availability in the cluster and the https://prow.k8s.io probe validates that the DNS is working.)
2. The two go.k8s.io probes are failing to follow redirects even though we have explicitly specified that redirects should be followed:
   

   test-infra/prow/cluster/monitoring/blackbox_prober.yaml

   Line 44 in b4a6cf7

   no_follow_redirects: false

   
   This is due to this blackbox exporter bug Redirect to different HTTPS host broken prometheus/blackbox_exporter#237 which should be resolved by Better handling of HTTP redirects. prometheus/blackbox_exporter#530, but there has not been a release cut since that fix merged: https://github.com/prometheus/blackbox_exporter/releases
   Resolving this for now by using the redirect URLs.

[cjwagner]

/assign @stevekuznetsov @hongkailiu

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cjwagner, stevekuznetsov

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• prow/cluster/monitoring/OWNERS [cjwagner,stevekuznetsov]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment