helm: allow user to configure gotemplate

[josedonizetti]

The helm config file allow a user to configure a value to a goTemplate, that can be used on the webhook, though tracee doesn't have access to such a file as it was not created with the tracee docker image. So, let's implement a way for the user to pass his template file, which can be configured as a configmap, and mounted on the tracee daemonset.