embed specific envbuilder version in binary

[johnstcn]

To accurately replicate a cached image, you need the exact envbuilder binary that was used to build it.

get cached image: error probing build cache: failed to optimize instructions: failed to get files used from context: failed to get fileinfo for /tmp/cached-image-data-source2380922079/.devcontainer/.envbuilder/bin/envbuilder: lstat /tmp/cached-image-data-source2380922079/.devcontainer/.envbuilder/bin/envbuilder: no such file or directory

Options:

1. go:embed the envbuilder binary
2. Fetch and extract the envbuilder binary from the envbuilder image dynamically.
3. Make kaniko lie about the tag it pushes so that it actually refers to the previous layer and not the one that adds /.envbuilder/bin/envbuilder.

1 is the most efficient option, but the most annoying.
2 adds some delay as this will have to be done at runtime but is the most flexible.
3 is kinda gross...