Docs updates from release test 10.0

[naisila]

DESCRIPTION: Docs updates after release testing for Citus 10.0

I tested the Use-Case Guides, Administer and Troubleshoot sections. (I went out of these sections only for the However to However, changes, with a find-replace in the whole repo)

Mainly some outdated outputs, partitioned table description, some small typos.

I also put the UTF8 encoding warning since I experienced issues with my database setup because it had SQL_ASCII encoding.

[jonels-msft]

@naisila thanks for the great changes. I left a few comments of things to change/check.

Also, I learned my lesson to add commas after "however." 😆

[jonels-msft]

Thank you!