[feature] add support for hinting via api/v_/instance preferred image / video max sizes

[NyaaaWhatsUpDoc]

Description

When left unset, defaults to local max size. The reason i didn't actually add local-image-max-size and local-video-max-size is in doing that it potentially opens us up for requiring local-audio-max-size, and potentially any other file types that we separate on in the future. It makes more sense to have a single local max size, and allow tweaking the frontend hinting that applications like Tusky use for autosizing.

It also updates the unused media limits (framerate, image / video dimensions) to just be the maximum possible int sizes. In case Tusky does try to limit based on those since we can support anything under the local max size.

closes #3449

Checklist

• [x] I/we have read the GoToSocial contribution guidelines.
• [x] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
• [x] I/we have not leveraged AI to create the proposed changes.
• [x] I/we have performed a self-review of added code.
• [x] I/we have written code that is legible and maintainable by others.
• [x] I/we have commented the added code, particularly in hard-to-understand areas.
• [x] I/we have made any necessary changes to documentation.
• [ ] I/we have added tests that cover new code.
• [x] I/we have run tests and they pass locally with the changes.
• [x] I/we have run go fmt ./... and golangci-lint run.