Update ActivityPubFetchService, fix authorized_fetch support

[dansup]

Closes #1850, #2713 and #2935

[ThatOneCalculator]

As per https://w3c-ccg.github.io/security-vocab/contexts/security-v1.jsonld , Misskey/Calckey actually use sec: prefixes for secure fetch signatures: https://codeberg.org/calckey/calckey/src/commit/e53d1f6bdc6fbb8da2d0b75c1b294708e7244058/packages/backend/src/remote/activitypub/misc/contexts.ts#L99-L137

Is there a reason for using toot:Ed25519Signature, toot:Ed25519Key etc?

[trwnh]

Ed25519Signature is not the same as Ed25519Signature2018. the former is taken from mastodon's context for end-to-end encrypted messaging, which was added in mastodon 3.2.0 (and i'm guessing dansup copied the context directly from mastodon): https://github.com/mastodon/mastodon/blob/9caa0475f891ded573739cd00e7bc915b31abb12/app/helpers/context_helper.rb#L24

additionally, the exact prefixes should not matter; term ids should be expanded to the full IRI as defined by @context. if calckey is using Ed25519Signature2018 for anything, they should be prepared to accept https://w3id.org/security#Ed25519Signature2018 as the unambiguous id for that.