This patch adds 2nd class support for hooks using julia as the language.
pre-commit will install any dependencies defined in the hooks repo
`Project.toml` file, with support for `additional_dependencies` as well.
Julia doesn't (yet) have a way to install binaries/scripts so for julia
hooks the `entry` value is a (relative) path to a julia script within
the hooks repository. When executing a julia hook the (globally
installed) julia interpreter is prepended to the entry.
Example `.pre-commit-hooks.yaml`:
```yaml
- id: foo
name: ...
language: julia
entry: bin/foo.jl --arg1
```
Example hooks repo: https://github.com/fredrikekre/runic-pre-commit/tree/fe/julia
Accompanying pre-commit.com PR: https://github.com/pre-commit/pre-commit.com/pull/998Fixes#2689.
