Introduce a new workflow which simplifies backporting

[ampresent]

The traditional workflow of Plugsched is,

• Generate scheduler module source code from a kernel binary A.
• Develop upon the generated scheduler module source.
• Building scheduler module.
• Install scheduler module onto a system running kernel binary A.

But @dtcccc comes up with another workflow,

• Given two kernel binaries A & B.
• Check scheduler module compatibility between A & B.
• Generate scheduler module source code from a kernel binary A.
• Building scheduler module.
• Install scheduler module onto a system running kernel binary B.

This new workflow largely simplifies backporting.