contint: Zuul status learned to query a single change

The Zuul status page learned to expose the status of a single change
with an URL such as /status/change/X,Y. The related upstream change is
https://review.openstack.org/#/c/124390/

 he daemon on gallium runs behind an Apache proxy which has a whitelist
of URL patterns.

Add a pattern that matches a Gerrit (change, patchset) such as 1234,1
limiting the lenght of the arguments to prevent potentially nasty usage.
The pattern accepts up to a billion change and 999 patchsets which
should be fine.

Bug: 47609
Change-Id: Ic5016371b40457d36acf56054bd6440b5cd5585d
Merge "contint: Zuul status learned to query a single change" into production