p2p: make persistent prop independent of conn direction (#3593)

## Description

Previously only outbound peers can be persistent.

Now, even if the peer is inbound, if it's marked as persistent, when/if conn is lost,
Tendermint will try to reconnect. This part is actually optional and can be reverted.

Plus, seed won't disconnect from inbound peer if it's marked as
persistent. Fixes #3362

## Commits

* make persistent prop independent of conn direction

Previously only outbound peers can be persistent. Now, even if the peer
is inbound, if it's marked as persistent, when/if conn is lost,
Tendermint will try to reconnect.

Plus, seed won't disconnect from inbound peer if it's marked as
persistent. Fixes #3362

* fix TestPEXReactorDialPeer test

* add a changelog entry

* update changelog

* add two tests

* reformat code

* test UnsafeDialPeers and UnsafeDialSeeds

* add TestSwitchDialPeersAsync

* spec: update p2p/config spec

* fixes after Ismail's review

* Apply suggestions from code review

Co-Authored-By: melekes <anton.kalyaev@gmail.com>

* fix merge conflict

* remove sleep from TestPEXReactorDoesNotDisconnectFromPersistentPeerInSeedMode

We don't need it actually.

rpc/core/pipe.go

@@ -44,7 +44,8 @@ type transport interface {
 }
 
 type peers interface {
-	DialPeersAsync(p2p.AddrBook, []string, bool) error
+	AddPersistentPeers([]string) error
+	DialPeersAsync([]string) error
 	NumPeers() (outbound, inbound, dialig int)
 	Peers() p2p.IPeerSet
 }