build-node-image: add more info to slack message

[dustymabe]

Let's at least put in the message the unique tag we apply to the node-image that has a timestamp in it.

build-node-image #456 :jenkins: :ocean: [4.20-9.6] master@b8e9016 (4.20-9.6-202505291554-node-image)

or maybe would be better to apply just the timestamp. I'm really not sure which I prefer.

build-node-image #456 :jenkins: :ocean: [4.20-9.6] master@b8e9016 (202505291554)

Another cool idea would be to add a quay emoji that links to the pullspec for that image so that we can just right click and copy/paste it to use it. This would be way more important if we choose the "only timestamp" option above.