Add extra /manager5 url route to serve local javascript files

Add extra /manager5 url route to serve local javascript files

Provided you symlink the manager5 directory to your git repository,
this will allow to test javascript changes by simply reloading
the page, without calling "make install" in between.
For instance, if you have your pve-manager code in $HOME/pve/pve-manager,
you can do

ln -s $HOME/pve/pve-manager/www/manager5 /usr/share/pve-manager/manager5

and you can serve javascript files directly from your copy of the source repo

curl -k -s -o /dev/null -w "%{http_code}" https://localhost:8006/pve2/manager5/Utils.js && printf "\n"
200

Not that at the momment this is only meant for Ext 5 development

Signed-off-by: Emmanuel Kasper <e.kasper@proxmox.com>