[BE][Help wanted] Automatically apply tags to backends

[xuzhao9]

We want to provide API to deal with user queries like:

• all custom Triton kernels
• all PT2-Triton kernels
• all Triton kernels, custom and PT2
• all CUTLASS kernels
• all operators that has both Triton and CUTLASS
• ...

To do that, we need to apply tags to kernels, like "cutlass", "triton", "pt2", "custom-triton", etc.
Tags can be added by identifying keywords in the backend names, static analysis, or could be manually annotated.