Add "SharedTags" support to "diff-pr.sh"
Add "SharedTags" support to "diff-pr.sh"

Example output of this bashbrew template (assuming `hello-world` had been converted to use `SharedTags`):

```console
$ bashbrew cat --format "$sharedTagsListTemplate" --all | grep -vE '^$'
hello-world:latest -- hello-world:linux, hello-world:nanoserver
```

infosiftr/stackbrew,neo-technology/docker-official-images,dinogun/official-images,docker-solr/official-images,infosiftr/stackbrew,neo-technology/docker-official-images,docker-library/official-images,thresheek/official-images,docker-flink/official-images,docker-library/official-images,davidl-zend/official-images,robfrank/official-images,mattrobenolt/official-images,docker-library/official-images,robfrank/official-images,infosiftr/stackbrew,robfrank/official-images,docker-solr/official-images,chorrell/official-images,mattrobenolt/official-images,neo-technology/docker-official-images,docker-solr/official-images,chorrell/official-images,davidl-zend/official-images,docker-library/official-images,robfrank/official-images,docker-flink/official-images,31z4/official-images,docker-library/official-images,mattrobenolt/official-images,thresheek/official-images,chorrell/official-images,docker-library/official-images,31z4/official-images,31z4/official-images,davidl-zend/official-images,jperrin/official-images,docker-flink/official-images,jperrin/official-images,thresheek/official-images,neo-technology/docker-official-images,docker-solr/official-images,docker-library/official-images,infosiftr/stackbrew,thresheek/official-images,infosiftr/stackbrew,docker-flink/official-images,31z4/official-images,infosiftr/stackbrew,jperrin/official-images,docker-library/official-images,neo-technology/docker-official-images,infosiftr/stackbrew,jperrin/official-images,mattrobenolt/official-images,docker-flink/official-images,dinogun/official-images,chorrell/official-images,davidl-zend/official-images,robfrank/official-images,davidl-zend/official-images,docker-library/official-images,infosiftr/stackbrew,mattrobenolt/official-images,thresheek/official-images,thresheek/official-images,docker-solr/official-images,docker-flink/official-images,chorrell/official-images,jperrin/official-images,robfrank/official-images,mattrobenolt/official-images,robfrank/official-images,neo-technology/docker-official-images,thresheek/official-images,chorrell/official-images,infosiftr/stackbrew,thresheek/official-images,docker-solr/official-images,robfrank/official-images,davidl-zend/official-images,31z4/official-images,thresheek/official-images,dinogun/official-images,neo-technology/docker-official-images,docker-flink/official-images,docker-flink/official-images,jperrin/official-images,neo-technology/docker-official-images,docker-flink/official-images,davidl-zend/official-images,jperrin/official-images,docker-library/official-images,thresheek/official-images,dinogun/official-images,docker-flink/official-images,docker-flink/official-images,davidl-zend/official-images,thresheek/official-images,docker-solr/official-images,docker-solr/official-images,dinogun/official-images,docker-solr/official-images,31z4/official-images,thresheek/official-images,jperrin/official-images,docker-library/official-images,mattrobenolt/official-images,infosiftr/stackbrew,jperrin/official-images,davidl-zend/official-images,thresheek/official-images,robfrank/official-images,chorrell/official-images,31z4/official-images,docker-solr/official-images,jperrin/official-images,davidl-zend/official-images,docker-flink/official-images,davidl-zend/official-images,dinogun/official-images,31z4/official-images,docker-library/official-images,chorrell/official-images,robfrank/official-images,jperrin/official-images,31z4/official-images,31z4/official-images,infosiftr/stackbrew,robfrank/official-images,docker-flink/official-images,robfrank/official-images,dinogun/official-images,chorrell/official-images,31z4/official-images,docker-solr/official-images,docker-solr/official-images,robfrank/official-images,mattrobenolt/official-images,dinogun/official-images,neo-technology/docker-official-images,neo-technology/docker-official-images,docker-solr/official-images,thresheek/official-images,infosiftr/stackbrew,mattrobenolt/official-images,31z4/official-images,mattrobenolt/official-images,infosiftr/stackbrew,mattrobenolt/official-images,dinogun/official-images,chorrell/official-images,neo-technology/docker-official-images,chorrell/official-images,docker-library/official-images,chorrell/official-images,infosiftr/stackbrew,mattrobenolt/official-images,neo-technology/docker-official-images,dinogun/official-images,dinogun/official-images,davidl-zend/official-images,31z4/official-images,neo-technology/docker-official-images,chorrell/official-images,docker-library/official-images,davidl-zend/official-images,31z4/official-images,jperrin/official-images,mattrobenolt/official-images,docker-solr/official-images,jperrin/official-images,neo-technology/docker-official-images,dinogun/official-images,dinogun/official-images