External packages

[gparmer]

Summary of this Pull Request (PR)

Add description here.

Intent for your PR

Choose one (Mandatory):

• [ ] This PR is for a code-review and is intended to get feedback, but not to be pulled yet.
• [x] This PR is mature, and ready to be integrated into the repo.

Reviewers (Mandatory):

@betahxy @WenyuanShao If you're interested. Mostly Rust and build system updates.

Can

./cos compose composition_scripts/external_hello_world.toml test
./cos run test

And it will run the component defined in https://github.com/gparmer/hello_world

The composition scripts have the repo directive:

[system]
description = "Test for the hello world external component"

[[components]]
name = "hw1"
img  = ""
repo = "github:gparmer/hello_world"
deps = [{srv = "kernel", interface = "init", variant = "kernel"}]
constructor = "kernel"

Existing scripts should run as expected.

Code Quality

As part of this pull request, I've considered the following:

Style:

• [x] Comments adhere to the Style Guide (SG)
• [x] Spacing adhere's to the SG
• [x] Naming adhere's to the SG
• [x] All other aspects of the SG are adhered to, or exceptions are justified in this pull request
• [ ] I have run the auto formatter on my code before submitting this PR (see doc/auto_formatter.md for instructions)

Code Craftsmanship:

• [x] I've made an attempt to remove all redundant code
• [x] I've considered ways in which my changes might impact existing code, and cleaned it up
• [x] I've formatted the code in an effort to make it easier to read (proper error handling, function use, etc...)
• [x] I've commented appropriately where code is tricky
• [x] I agree that there is no "throw-away" code, and that code in this PR is of high quality