custom metadata nodes

[parsee-mizuhashi]

(continuation of #8737 since i dont know how to git, my bad)

explanation of what the nodes do:
GetWorkflowMetadata: gets the pnginfo metadata (e.g. the one saved by default in SaveImage
EmptyMetadata: makes a new empty metadata to add upon
AddMetadataValue: adds a new value to the metadata
SaveImageCustomMetadata: saves image with custom metadata

this time its defined with v3 spec, ty comfy for showing me how to do do pnginfo in v3 spec
(note: should prob replace custom type with another type? feels too niche to require a whole new type so left it just as a custom type, also might help people making v3 nodes in the future)

[Kosinkadink]

Since the metadata is a special type that would be supported by core, assuming it will be accepted, the type should be defined within _io.py of latest API (comfy_api/latest/_io.py). Nice to see nodes written in v3 schema lol.

[asagi4]

Is the PngInfo object sufficient to contain metadata for all filetypes that could contain metadata? Maybe it could use a custom container type instead so you could extend the system to more than just images, like safetensors files or videos, without having to have separate types for all of them.

[parsee-mizuhashi]

Since the metadata is a special type that would be supported by core, assuming it will be accepted, the type should be defined within _io.py of latest API (comfy_api/latest/_io.py). Nice to see nodes written in v3 schema lol.

will add the custom type into the _io.py file then

Is the PngInfo object sufficient to contain metadata for all filetypes that could contain metadata? Maybe it could use a custom container type instead so you could extend the system to more than just images, like safetensors files or videos, without having to have separate types for all of them.

i mostly intended this as just a way to give images custom metadata, but will try and add webm / checkpoint metadata