Add pixi self-update

[hadim]

Supersede #582

---

You can test it locally in your dev env with:

$ pixi run cargo run -- self-update --force --version 0.8.0
$ ./target/debug/pixi --version
pixi 0.8.0

---

See the current API:

$ pixi self-update
✔ Pixi will be updated from '0.1.0' to '0.12.0'
✔ Pixi archive downloaded.
✔ Pixi archive uncompressed.
✔ Pixi has been updated to version 0.12.0.

$ pixi self-update # wrong pixi location
✘ pixi is not installed in the default location:
- Default pixi location: /Users/hadim/.pixi/bin/pixi
- Pixi location detected: /Users/hadim/Code/libs/pixi/pixi/target/debug/pixi

It can happen when pixi has been installed via a dedicated package manager (such as Homebrew on macOS).
You can always use `pixi self-update --force` to force the update.

$ pixi self-update --version 0.8.0
✔ Pixi will be updated from '0.1.0' to '0.8.0'
✔ Pixi archive downloaded.
✔ Pixi archive uncompressed.
✔ Pixi has been updated to version 0.8.0.

$ pixi self-update
✔ pixi is already up-to-date (version 0.12.0)

$ pixi self-update --version 0.8.99
✘ The version you specified is not available: 0.8.99

[wolfv]

I am happy with the logic. I'll let Bas and Ruben chime in with their thoughts!

[hadim]

@baszalmstra ready for another round!

I removed all the unwrap and replaced most of them by except (when the error is quite unlikely to happen).

I am also now using miette for "expected" errors.

I also replaced all the println to eprintln.

[hadim]

I also replaced all the println to eprintln.

I am actually unsure whether those should be printed to stdout or stderr looking at other cli commands.

[baszalmstra]

Some small nitpicks but looks good to me!

[hadim]

Thanks @baszalmstra - should be good now.

[wolfv]

@hadim maybe you can follow up with a few docs. Great feature! :)

[hadim]

@hadim maybe you can follow up with a few docs. Great feature! :)

I already added the cli doc at docs/cli.md in that PR. Do you mean something else?

[wolfv]

perfect, nope. sorry. didn't look closely enough 🤦 (getting late over here haha)