[Feature] Add "set this image as..." in image operations menu

[echo6ix]

trafficstars

Let users set a tag image or performer image directly from the operation menu of an image in the Stash image library.

Off the top of my head this could be accessible in the following way via the operation menu

Images section > click an image > click the operation menu > available options: Set this image as tag... and Set this image as performer...

Either option could open some kind of filtered list to search for the respective items.

[seducingbits]

Another option could be Set this image as gallery cover.

[YurikaL]

Related issue about gallery cover: #863