Releasing version 2.9.1

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TASK: helper script to help setup e2e tests locally

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BUGFIX: disable submiting inspector in invalid state with
BUGFIX: Prevent infinite refresh loop
BUGFIX: Make loading bar visible
BUGFIX: createNew doesn't set title of new node
BUGFIX: Backend tables center text
BUGFIX: fix empty CKE5 StyleSelect when no headings are allowed (

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DOCS: add 2.x to upmerge instructions

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Many thanks to all Contributor:

@christophengelmayer @dimaip @gerhard-boden

All changes in this release: 2.9.0...2.9.1