add Homebrew on Linux (#589)

* Add homebrew installation and validation scripts

* Update `/etc/environment` in `updatepath.sh` script

Keep this code for sake of compatibility with the existing installation logic. It will be changed in its own PR

* Remove env. variables from homebrew validation task

* Move reboot to the dedicated script and task

Co-authored-by: Sergey Dolin <v-sedoli@micorosoft.com>

images/linux/scripts/helpers/document.sh

@@ -9,7 +9,7 @@ function WriteItem {
         echo "METADATA_FILE environment variable must be set to output to Metadata Document!"
         return 1;
     else
-        echo -e "$1" >> "$METADATA_FILE"
+        echo -e "$1" | sudo tee -a "$METADATA_FILE"
     fi
 }