cargo: make jj installable with cargo binstall

[ilyagr]

(This is mainly a draft because it is based on #2277)

https://github.com/cargo-bins/cargo-binstall

Note that jj will only become installable once the next release
is published to crates.io. For this reason, I am planning to
wait until then before documenting the fact that jj can be
installed this way.

At that point, cargo binstall jj-cli should be sufficient.

Before then, it's possible to test that this will work by doing

cargo binstall jj-cli --force --strategies crate-meta-data \
   --log-level debug  --dry-run --manifest-path cli/Cargo.toml

Without --dry-run, this should install the 0.9 release if run
on cli/Cargo.toml form this commit. (You don't need the rest
of the jj repo for this to work, you can just download the
Cargo.toml and point --manifest-path to it)

Checklist

If applicable:

• I have updated CHANGELOG.md
• I have updated the documentation (README.md, docs/, demos/)
• I have updated the config schema (cli/src/config-schema.json)
• I have added tests to cover my changes