connlib: moves it to the main firezone library

This brindgs connlib from its own separated repo to firezone's monorepo.
    
 On top of bringing connlib we also add and unify the Dockerfile for all
 rust binaries and add a docker-compose that can run a headless client, a
 relay and a gateway which eventually will test the whole flow between a
 client and a resource. For this to work we also incorporated some elixir
 scripts to generate portal tokens for those components.

elixir/.gitignore

@@ -1,6 +1,3 @@
-# macOS cruft
-.DS_Store
-
 # HTTPS dev certs
 priv/pki/authorities/local/
 
@@ -16,9 +13,6 @@ deps/
 # If the VM crashes, it generates a dump, let's ignore it too.
 erl_crash.dump
 
-# If NPM crashes, it generates a log, let's ignore it too.
-npm-debug.log
-
 # The directory NPM downloads your dependencies sources to.
 /assets/node_modules/