snippet-sharing: fixes + tutorial improvements

[Namoshek]

Purpose

This PR solves the issues in #1160.

Checklist

Please only check relevant points.
For docu fixes, spell checking and similar nothing
needs to be checked.

• commit messages are fine (with references to issues)
• I ran all tests and everything went fine
• affected documentation is fixed
• I added unit tests
• I added code comments, logging, and assertions
• meta data is updated (e.g. README.md of plugins)

@markus2330 please review my pull request

[markus2330]

Any reason to do here differently? Maybe validation will be added later? Or we should always do validation (even when setting per namespace).

[markus2330]

Thank you! The question was too general to address in this PR, should we open an extra issue for this?

[Namoshek]

You are actually right, I could have written it with some view into the future.

Doing validation always seems a good idea and shouldn't be difficult to implement for the kdb tool.

[markus2330]

Thanks, you are right, I opened #1164.

Btw. there is also #886 which would allow you to always issue kdb global-mount (if other plugins are already mounted, it would be a NOP)