Create a new export documents meilitool subcommand

[Kerollmops]

This subcommand can be useful for extracting documents from an existing database.

[Kerollmops]

Hey @dureuill 👋 I fixed the issue and added support for vectors. Can you review that again? 🙂

[dureuill]

I can accept the changes as-is, but I'm wondering if we should maybe factor the logic to export the documents between meilitool and the dumps:

this logic changed multiple times (most recently, to inject vectors) and now exists in two different locations. If the next change updates the index-scheduler but forgets about meilitool, then we will get possibly hard to track inconsistencies when using the meilitool export-documents command.

If factoring the logic is too complicated due to them being in different crates not using the same types, maybe a comment on the index-scheduler implementation to also implement the meilitool implementation would be welcome.

What do you think?

The base branch was changed.

[dureuill]

thank you so much!

bors merge

[meili-bors]

Build succeeded:

• Run tests in debug
• Tests on ubuntu-20.04
• Run Clippy
• Tests on macos-13
• Run Rustfmt
• Tests on windows-2022