Fix/rework update instructions (including Elasticsearch update)

[AnonymousWP]

This title doesn't say much on its own. I was encountering the following: documentation tells me to import the 7.x repo and install ElasticSearch, while that's not even working for Zammad 6.x: https://docs.zammad.org/en/latest/prerequisites/software.html#elasticsearch-optional

Or am I interpreting it wrong?

[ralf401]

Yes our documentation seems outdated. I created a separate issue for that and will fix it.

[AnonymousWP]

The table above hasn't been fixed/reworked in the PR. 🤔

[MrGeneration]

The table is up to date. Elasticsearch 7.8+ and 8 are supported.