[llvm] Improve the pull-request subcription notification format by adding the description and files statistics (PR #65828)

[Mehdi Amini via llvm-commits]

joker-eph wrote:

See https://github.com/llvm/llvm-project/pull/65439#issuecomment-1712368466 for a test

https://github.com/llvm/llvm-project/pull/65828