FR: Option to turn off image present auto-generation

[FrittenKeeZ]

Is your feature request related to a problem? Please describe.
If you have 3000+ images and 6 image presets, but don't use all presets for every image, you end up using a lot more storage than necessary.

Describe the solution you'd like
An option to turn off image preset auto-generation, so an image preset is only created when needed.

Describe alternatives you've considered
A small addon which disables preset auto-generation.

[jasonvarga]

Workaround outlined in #2321 (comment)

[jasonvarga]

Also, added an option to 2.11.4.

Add image_manipulation_presets_generate_on_upload: false to assets.yaml