Create a generic reply kind

[basantagoswami]

Replies to a kind:1 plaintext note are also kind:1, which creates the issue of not being able to find just "root" kind:1 events. But unfortunately it's not very easy or convenient to change it anymore.

But for all the other kinds of replies, we can specify or try to use a generic reply kind. These events must have at least one e or a tag, (and also at least one p tag?). They can be used for making comments on:

• git patches
• long form articles
• live streams and nest audio channels
• public channels (can be used for messages there)
  etc

These are just examples, but we don't have to change anything in existing meta-protocols, if they already have a different kind for their replies/comments. But having it specified means, any new meta-protocol that we create can use this event kind for their replies/comments.

[alexgleason]

This is related to #523 #683

The new Groups NIP has separate kinds for replies. Not sure I agree with it.