enhance: Embedded all attachment, renotes and discussion history into rss feed content & improve title

[CGsama]

What

The feed npm module dose not support multiple files, and enclosure format may not parse correct by apps, so that embedding all files into content. Also the email field is required by some app, so add a dummy one, could improved by use user email if have one.

The feed also can track back x posts for reply and renote, by using query string e.g. https://xxx/@xxx.atom?history=5 will include 5 most recent notes in the thread

Why

Resolve #7004

Additional info (optional)

Change originally made for #6696 at v11, now port to v12 to match file structure, working fine on my instance for years

[CGsama]

query example: https://xxx.xxx/@xxx.atom?thread=3&history=5&noteintitle&norenotes&noreplies

thread: how deep a thread can go (reply history) history: how many notes totaly noteintitle: put note content in title norenotes: no renotes in feed noreplies: no noreplies in feed

[CGsama]

anything needs to change/fix?

[CGsama]

Any updates here? Thx

[CGsama]

rebase to latest

[tamaina]

Close because it has been moved to FeedService and conflicted heavily. (I wonder how @syuilo can do such a terrible thing)