RFE: Merge weekly scanning result emails per-image

[aditya-konarde]

I maintain multiple mattermost images on the container index here

With the weekly scan, I recently got multiple emails titled Weekly scanning results for image: <imagename>

I think it would be better UX if emails for the results of the same image are combined.

For example:
Image:mattermost-server tag:5.0 and Image:mattermost-server tag:5.1 results should be combined in a single mail
Image:mattermost-foo-integration is a different image so the mail goes separately.

This will reduce the number of mails going to the inbox of someone maintaining multiple tags for the same image.