feat: add pixi upgrade

[Hofer-Julian]

Design proposal: #912

Implementation in this PR:

# Resolve all the dependencies of the default feature without any constraints and installs the solved solution.
pixi upgrade 

# Resolve a specific dependency
pixi upgrade package

# Resolve multiple dependencies
pixi upgrade package_a package_b

# Upgrade all dependencies in a single feature
pixi upgrade --feature test

# Upgrade all dependencies except python and julia
pixi upgrade --exclude python --exclude julia

# Run upgrade logic without writing to disk
pixi upgrade --dry-run

# Run upgrade and get output in json format
pixi upgrade --json

This PR is important as it is not easy enough right now to update a full setup with pixi as it automatically pins most of your dependencies to a major or minor version.

[ruben-arts]

Tested it while adding some small features. Works great!