Log Message:
mitmproxy: Update to 5.3.0

Changes:
5.3.0
=====
* Support for Python 3.9 (@mhils)
* Add MsgPack content viewer (@tasn)
* Use `@charset` to decode CSS files if available (@prinzhorn)
* Fix links to anticache docs in mitmweb and use HTTPS for links to
  documentation (@rugk)
* Updated typing for WebsocketMessage.content (@prinzhorn)
* Add option `console_strip_trailing_newlines`, and no longer strip trailing
  newlines by default (@capt8bit)
* Prevent transparent mode from connecting to itself in the basic
  cases (@prinzhorn)
* Display HTTP trailers in mitmweb (@sanlengjingvv)
* Revamp onboarding app (@mhils)
* Add ASGI support for embedded apps (@mhils)
* Updated raw exports to not remove headers (@wchasekelley)
* Fix file unlinking before external viewer finishes loading (@wchasekelley)
* Add --cert-passphrase command line argument (@mirosyn)
* Add interactive tutorials to the documentation (@mplattner)
* Support `deflateRaw` for `Content-Encoding`'s (@kjoconnor)
* Fix broken requests without body on HTTP/2 (@Kriechi)
* Add support for sending (but not parsing) HTTP Trailers to the HTTP/1.1
  protocol (@bburky)
* Add support to echo http trailers in dumper addon (@shiv6146)
* Fix OpenSSL requiring different CN for root and leaf certificates (@mhils)
* ... and various other fixes, documentation improvements, dependency
  version bumps, etc.