Add 0.4.21 CHANGELOG

Co-Authored-By: Michael Avila <michaelavila@users.noreply.github.com>

Co-Authored-By: Dominic Della Valle <ddvpublic@Gmail.com>

Co-Authored-By: MollyM <momack2@users.noreply.github.com>

WIP. Please either add or mention in comments what should be featured.

License: MIT
Signed-off-by: Jakub Sztandera <kubuxu@protonmail.ch>

fix: use http.Error for sending errors

This sets a few headers that prevent browsers from misinterpreting the error
text.

core: call app.Stop once

explain what dhtclient does

release: v0.4.21-rc3

This time, we'll actually build it.

fix race between adding tags and registering services with the connection manager

Hopefully helps fix #6271 and a bunch of other related issues.

disable write coalescing

See: https://github.com/libp2p/go-libp2p/issues/644

release: go-ipfs 0.4.21-rc2

remove yamux read buffer

The current version has some build issues.

Accidentally added in #6361. The yamux transport now disables this globally by
default.

dep: update yamux and bitswap

* yamux: reduce goroutines per connection from 3 to 2.
* bitswap:
  - fix a very slow memory leak
  - adds an option for disabling providing (unused for now)
  - fixes a race condition on start
  - tag peers with outstanding requests in the connection manager

dep: update go-libp2p

* Write coalescing in yamux and mplex.
* Correctly tag relay streams.
* Reset relay streams instead of closing them. Fixes #6237.
* Trim connections in a background task instead of on-connect.

ci: actually enable golangci-lint

commands/swarm(fix): handle empty multiaddrs

Forbids empty multiaddr, fixes #6354

release v0.4.21-rc1