Add trailing slash to Omnibus wss address links

What does this MR do?

Modifies the Omnibus kas-address shown in various places to have a trailing /.

Same rationale as !55565 (merged) which fixed some occurrences but unfortunately missed the others. This change makes all references consistent.

Background:

When KAS is enabled on the GL instance the following config is added to /var/opt/gitlab/nginx/conf/gitlab-http.conf which expects the trailing / to be present in requests from the agent:

  location /-/kubernetes-agent/ {
    proxy_pass http://localhost:8150/;
  }

If it isn't, the GL instance responds with a redirect and this generates the following error on the agent:

{"level":"error","time":"2021-03-01T21:13:05.380Z","msg":"Reverse tunnel","mod_name":"reverse_tunnel","error":"Connect(): rpc error: code = Unavailable desc = connection error: desc = \"transport: Error while dialing failed to WebSocket dial: expected handshake response status code 101 but got 301\""}

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