[META] Documentation plan for Beta v1.0.0

[pebrc]

Moving to StatefulSet-based orchestration, some of the current documentation is no longer accurate and the following updates are required:

• Add a new section about node orchestration - Add a new section about node orchestration (StatefulSet related) #1758 (@sebgl, @barkbay, @pebrc)
• Add a new section "Running Kibana on ECK" - Kibana docs #1389 (@barkbay)
• Add a glossary - ECK short glossary #1744 (@alaudazzi)
• Update Node scheduling section - Refresh the "Node scheduling" doc based on StatefulSet #1763 (@sebgl)
• Update strategy section - Refresh the "Update strategy" doc based on StatefulSet  #1762 (@david-kow)
• Update Troubleshooting section - Update the Troubleshooting section with StatefulSet info #1761 (@thbkrkr)
• Remove redundancies between JVM heap size and Managing compute resources - Update heap size and compute resources documentation #1785 (@charith-elastic)
• Remove Group Definition section - Remove grouping definition from the update strategy #1751 (@thbkrkr)
• Upgrade your cluster - Upgrade your cluster #1143, Topology changes reference doc #1144 (@sebgl)
• Document operator configuration options - Document operator configuration options #1379 (@anyasabo)
• Make ECK requirements more explicit in the documentation - Make ECK requirements more explicit in the documentation #1858 (@alaudazzi)
• Make k8s nodes vs. Elasticsearch explicit in docs - Make k8s nodes vs. Elasticsearch explicit in docs #1851 (@anyasabo)
• Updated the cloud-on-k8s README.md - Updated the cloud-on-k8s README.md #1890 (@alaudazzi)

[sebgl]

As per #1736 (comment), let's not forget to document that PVCs are removed automatically.

[alaudazzi]

Relates to #1758