Add paths for serving attachment content in IssueTracker

We're moving to serve attachments from subdomains of the product
domains. For example, for issues served from
issuetracker.google.com, attachments will be served from
usercontent.issuetracker.google.com. For issues served from 
g-issues.skia.org or issues.skia.org, we want to serve attachments 
in those issues from usercontent.g-issues.skia.org and 
usercontent.issues.skia.org.

Bug: 365835307

Change-Id: I1b0cb0b3e103ef084a954ddc5d11674b58577e8b
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/927679
Commit-Queue: Richard Collett <[email protected]>
Reviewed-by: Kaylee Lubick <[email protected]>

Author: Richard Collett

skfe/skia.org.zone

@@ -92,8 +92,10 @@ url9405       300 IN CNAME sendgrid.net.
 26644806      300 IN CNAME sendgrid.net.
 
 ;;; Buganizer custom domains for Skia.
-issues     300     IN CNAME www3.l.google.com.
-g-issues   300     IN CNAME uberproxy.l.google.com.
+issues               300 IN CNAME www3.l.google.com.
+g-issues             300 IN CNAME uberproxy.l.google.com.
+usercontent.issues   300 IN CNAME www3.l.google.com.
+usercontent.g-issues 300 IN CNAME uberproxy.l.google.com.
 
 ;;; CNAME all the hosts for this domain.
 *          3600    IN CNAME skia.org.