Docker image should run non-root (#153)

Changed the Dockerfile so that there is a Inbucket user (and group). This will allow the container to be executed a the Inbucket user in stead of ROOT (security best practices)

If the user wants to use a different greeting.html file he can use the environment variable to define a different one. For now we just use the greeting.html from the defaults directory.

* Permissions for /start-inbucket.sh file
* Added timezone data so you can set the timezone in the image
* Updated Docker greeting.html file to include some basic instructions
* Updated to alpine 3.11
* Updated to golang 1.14
* Updated the required packages

etc/docker/defaults/start-inbucket.sh

@@ -3,22 +3,7 @@
 # description: start inbucket (runs within a docker container)
 
 INBUCKET_HOME="/opt/inbucket"
-CONF_SOURCE="$INBUCKET_HOME/defaults"
-CONF_TARGET="/config"
 
 set -eo pipefail
 
-install_default_config() {
-  local file="$1"
-  local source="$CONF_SOURCE/$file"
-  local target="$CONF_TARGET/$file"
-
-  if [ ! -e "$target" ]; then
-    echo "Installing default $file to $CONF_TARGET"
-    install "$source" "$target"
-  fi
-}
-
-install_default_config "greeting.html"
-
 exec "$INBUCKET_HOME/bin/inbucket" $*