Add support for feature order definition in devcontainer definitions

[kujenga]

Currently, the order that features are executed as part of the container build is alphabetically sorted in the following code, where there is a TODO to implement support for the "installation order" that is part of the devcontainer spec: https://containers.dev/implementors/features/#installation-order

https://github.com/coder/envbuilder/blob/c72728897e91e713958a8ca0c7211574784ae79e/devcontainer/devcontainer.go#L236-L244

The ask in this issue is to implement support for:

• The dependsOn property defined as a part of a Feature’s devcontainer-feature.json.
• The installsAfter property defined as part of a Feature’s devcontainer-feature.json.
• The overrideFeatureInstallOrder property in user’s devcontainer.json. Allows users to control the order of execution of their Features.

I wasn't able to find an existing issue tracking this, but let me know if there is! Happy to also provide more context on why this is a useful feature if that helps in prioritizing this. Features with any sort of dependencies are unusable in most cases unless the alphabetical ordering happens to line up.

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In the meantime, it would be helpful to have this documented in the way that this PR did for other unsupported features: https://github.com/coder/envbuilder/pull/219