New 2.9 errors

[michaelstingl]

2.9 came with some new error messages, and they're not easy to resolve. 2.9.1 error messages will link to this page.

Issues:

• [FAQ] Explain error message about Multiple account are sharing the folder #102
• Add error codes to error messages client#9005

Testing the PR

git clone git@github.com:owncloud/docs-client-desktop.git
cd docs-client-desktop
git checkout faq-errors
yarn install
yarn antora
yarn serve

Then you can find the changed version here:
http://localhost:8080/desktop/next/faq.html

TODO

• Add descriptions + solutions/workarounds
• Add consistent screenshots for each error after @TheOneRing implemented the links

Versions

• 2.9+

[mmattel]

...2.9.1 error messages will link to this page...

• In case you hardcode links from client to docs, I highly recommend NOT to use anchors to sections but pages only
• To be future proof, the core team uses a web server sided php script (go.php) like https://doc.owncloud.com/server/10.7/go.php?to=user-sharing-federated
  to access doc resources inside the core code to neutralize access.
  This makes it much easier to adopt targets without changing the source (the desktop client)
  You may create a renamed copy of the php script (like gd.php) at gitea and set the redirects in that script accordingly
• They core team recently added a check if links are valid, see: Move all doc-links to a collected space, Add command to verify all available doc links core#39026

[EParzefall]

I share Martin's concerns with using anchors. The script approach is better in case adjustments are necessary in the future. One place to rule them all.

[TheOneRing]

Typo in file name modules/ROOT/assets/images/faq/older-used-by-different-client.png

[michaelstingl]

@TheOneRing could you review the latest changes?

[TheOneRing]

LGTM

[michaelstingl]

@mmattel @EParzefall could you take over and bring this to life?

[EParzefall]

Some language improvements necessary