add V2.19 upgrade docs

docs/Upgrade-2.19.md

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+# Upgrade to KubeZero V2.19.0
+
+# CloudBender / Kubernetes v1.19
+## Changes
+- worker nodes names are now the default AWS private hostnames, rather than the CloudBender provided unique static hostnames :-(  
+This change was required to enable node restrictions via the upstream aws-iam-authenticator as well as prepare for support of the Horizontal Autoscaler and Spot Instances in the next releases 
+- cluster-admin kubectl config now stored on SSM Parameter store, contains no more secrets leveraging IAM roles
+- fully encrypted cluster backup on S3
+( automated migration and cleanup of previous files )
+- backup password and cluster version stored on SSM Parameter store
+- worker nodes authenticate via IAM roles rather than tokens
+- improved resource reservations on all nodes
+- various security / reliability improvements and bug fixes
+ 
+## Upgrade
+- Set Kubernetes version in the controller config to eg. `1.19`  
+- Update controller and worker stacks with latest CFN code
+
+- terminate controller00 first, afterwards remaining controllers
+- replace worker nodes in a rolling fashion via. drain / terminate / rinse-repeat
+
+# KubeZero
+## Changes
+- Version bump to latest releases of *EVERY* component
+- optional support for fuse-device-plugin
+- KubeZero now supports bare-metal, all AWS components optional
+- resource definitions for most admin pods, incl. apiserver, etcd, etc.
+- Logging:
+  - ES resources are now defined using standard config vs. custom settings like jvm_heap and cpu_request
+  - Optional ability to add nodeAffinity rules for ES/Kibana and Fluentd
+  - Fluentd replicaCount default from 2 to 1
+
+## Upgrade - Without ArgoCD
+### CRDs:
+( commands assume latest kubezero repository being checkout next to this git repository to deploy master / non-released version )
+  
+  `./bootstrap.sh crds all clusters/$CLUSTER ../../../kubezero/charts`
+
+### Components
+`./bootstrap.sh deploy all clusters/$CLUSTER ../../../kubezero/charts`
+
+## Upgrade - ArgoCD
+- push latest config to git repo
+- verify correct branch etc. ( argoless branch is retired ! )
+- trigger sync in ArgoCD starting with the KubeZero root app  
+( only if auto-sync is not enabled )
+
+## Verification / Tests
+- check if all pods are RUNNING
+- check any Ingress services
+- ...