imagestream: point centos7 images to quay.io

Use quay.io as a source of the images to avoid Docker Hub ratelimiting where possible

Author: vrutkovs

imagestreams/php-centos.json

@@ -102,7 +102,7 @@
         },
         "from": {
           "kind": "DockerImage",
-          "name": "docker.io/centos/php-73-centos7:latest"
+          "name": "quay.io/centos7/php-73-centos7:latest"
         },
         "referencePolicy": {
           "type": "Local"