Geo Documentation: Improve General Geo update steps

Problem to solve

Some sections of the Geo update instructions are ambiguous and should be rephrased.

Further details

https://docs.gitlab.com/ee/administration/geo/replication/updating_the_geo_nodes.html#general-update-steps

all you need to do is update GitLab itself:

This is not actually correct. I currently have to also update the tracking database on secondary nodes (see https://gitlab.com/gitlab-org/gitlab-ee/issues/12270) and test things. We may consider rephrasing this.

1. Log into each node (primary and secondary nodes).

I assume this means "to a console on your node". This can mean I have to open as many terminal sessions as there are Geo nodes. For large installations, this suggestion may cause confusion. Maybe this can be rephrased or removed as it is replicated later

• Reword documentation
• Define if the primary or the secondaries need to be upgraded first
• Decide if we should link directly to the Omnibus installation guide

Proposal

• We may be able remove step 3 completely
• We may be able to automate step 4

Who can address the issue

Other links/references