Realtime events V2 considerations and requirements

[gotson]

Komga supports realtime notifications using SSE (Server Sent Events), which is used by the webui but also by other apps like Komf.

While rewriting the UI, I noticed some shortcomings about the current implementation.

This is a list of what should be looked at when doing a new major version with breaking changes:

• evaluate whether clients could subscribe only to some events
• the ReadProgressSeriesChanged and ReadProgressSeriesDeleted events are only triggered when the whole series is marked as read/unread.
• the ReadProgressChanged, ReadProgressDeleted and BookImported events do not have the seriesId or libraryId fields.
• it is currently not possible to get older events, which SSE supports.
• the existing Historical Events API does not list the same events as the realtime feed, and the schema differs.
• the realtime feed should be documented in a similar way the REST API is.