buildx/controller/build
Brian Goff 98efe7af10 Support for passing through raw buildkit policies
This adds an env var which can be used to pass in a path to a file to
read a buildkit source poliy from.

This is applied to any build is executed with the env set.
It is also applied to bakes (which are calling build behind the scenes).

Signed-off-by: Brian Goff <cpuguy83@gmail.com>
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build.go Support for passing through raw buildkit policies