Update emacs in environment to be built from HEAD and support broadway

[hh]

Now that emacs-broadway can be reached via coderd, update our primary environment emacs-build to support using broadwayd:

It will require compiling emacs from src and adding --with-json=yes --with-modules=yes --with-native-compilation=yes --with-pgtk=yes --with-cairo=yes flags to ./configure.

• Working coder-template : add emacs-broadway template cncf-infra/coder-templates#10
• Required coder PR : fix: do not canonicalize Sec-WebSocket-* headers in apps coder/coder#5334

[BobyMCbobs]

@hh, moved to sharingio/environment