Settings: Make "Show a notification when executing shell commands" decidable on a per shell command basis

[Taitava]

Discussed in https://github.com/Taitava/obsidian-shellcommands/discussions/260

I just noticed the above function is implemented as a 'global' settings. Might be good to have it per command.

Originally posted by @snail123815 in https://github.com/Taitava/obsidian-shellcommands/discussions/260#discussioncomment-3894049

TODO:

• [x] Implement the thing.
• [x] Add to CHANGELOG.md.

[Taitava]

Done. Will be released in 0.22.0.

[Taitava]

This is now released.