[Docs] Beats upgrade and permissions

[leehinman]

Beats upgrading doc currently has:

https://github.com/elastic/beats/blob/a6aa347eeeb9a00524044036157788ce9eb3d0f0/libbeat/docs/upgrading.asciidoc?plain=1#L17-L21

We should add to it that if assets have changed (dashboards, pipelines, index templates, etc), then it will be necessary to run at least once with permissions that can do the setup operations.