[Documentation] Permissions required for elastic-package

[stevengoossensB]

We want to run elastic-package internally, targeting a specific stack to avoid having to recreate the stack continuously and to make use of some shared resources that are currently not supported (e.g. enrich policies). We would like to avoid using the superuser elastic, but I can't find documentation on the exact permissions required for such a user. Could you update the documentation and specify the roles and Kibana permissions required?