[enh] ability to edit watermark_id at thumbnailSizes in backend

[Philosoft]

In fact, there actually is exactly this feature, but it's hidden under option "use watermarks" in configuration - images :man_facepalming:

[fps01]

So... Issue is solved?

[Philosoft]

dunno. i gues we can close it for now, until we came up with any other solution at all or abandon it alltogether