[gen] Add gen alias command

[mikeland73]

Summary

Add a command that allows creating aliases to devbox scripts. This lets users source aliases from any project they want. It's opt-in, works in POSIX and fish. Aliases make it easy to call the scripts for other projects or directories.

How it works:

eval "$(devbox gen alias)"
devbox-build

It builds the alias name using the project name in devbox.json.

Alternatively the user can specify a prefix

eval "$(devbox gen alias --prefix dx)"
dx-build

How was it tested?

eval "$(devbox gen alias --prefix dx)"
dx-build
cd $HOME && dx-build

[gcurtis]

Sounds good to me!

[sentry-io]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

• ‼️ **Generic Error: <redacted errors.withStack>: <redacted usererr.combined> go.jetpack.io/devbox/internal/boxcli/usererr in... View Issue
• ‼️ **Generic Error: <redacted *errors.withStack>: <redacted errors.withStack>: <redacted usererr.combined> go.jetpack.io/devbox/internal/boxcli/usererr in... View Issue

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