[Feature] On hover display small performer image on performer dropdown selector form

[echo6ix]

Related to https://github.com/stashapp/stash/issues/2575, per Discord,

"Whoever implemented the tag card tooltips, considering doing the same for the performer dropdown lists. When adding performers manually, there's a point when you've accumulated so many, often with the same single name, that you really need an image tool tip to either remember who they are or to differentiate them"

• Show performer image when hovering over a performer name in the dropdown performer form for scenes/images/galleries edit pages.
• Add a toggle switch in the settings to enable/disable this functionality