Re-add follow recommendations API (#7918)

* Re-add follow recommendations API

    GET /api/v1/suggestions

Removed in 8efa081f21 due to Neo4J
dependency. The algorithm uses triadic closures, takes into account
suspensions, blocks, mutes, domain blocks, excludes locked and moved
accounts, and prefers more recently updated accounts.

* Track interactions with people you don't follow

Replying to, favouriting and reblogging someone you're not following
will make them show up in follow recommendations. The interactions
have different weights:

- Replying is 1
- Favouriting is 10 (decidedly positive interaction, but private)
- Reblogging is 20

Following them, muting or blocking will remove them from the list,
obviously.

* Remove triadic closures, ensure potential friendships are trimmed

app/models/concerns/account_interactions.rb

@@ -89,10 +89,13 @@ module AccountInteractions
                               .find_or_create_by!(target_account: other_account)
 
     rel.update!(show_reblogs: reblogs)
+    remove_potential_friendship(other_account)
+
     rel
   end
 
   def block!(other_account, uri: nil)
+    remove_potential_friendship(other_account)
     block_relationships.create_with(uri: uri)
                        .find_or_create_by!(target_account: other_account)
   end
@@ -100,10 +103,13 @@ module AccountInteractions
   def mute!(other_account, notifications: nil)
     notifications = true if notifications.nil?
     mute = mute_relationships.create_with(hide_notifications: notifications).find_or_create_by!(target_account: other_account)
+    remove_potential_friendship(other_account)
+
     # When toggling a mute between hiding and allowing notifications, the mute will already exist, so the find_or_create_by! call will return the existing Mute without updating the hide_notifications attribute. Therefore, we check that hide_notifications? is what we want and set it if it isn't.
     if mute.hide_notifications? != notifications
       mute.update!(hide_notifications: notifications)
     end
+
     mute
   end
 
@@ -194,4 +200,10 @@ module AccountInteractions
     lists.joins(account: :user)
          .where('users.current_sign_in_at > ?', User::ACTIVE_DURATION.ago)
   end
+
+  private
+
+  def remove_potential_friendship(other_account)
+    PotentialFriendshipTracker.remove(id, other_account.id)
+  end
 end