Build Triton in Docker image (#95233)
See a bunch of timeout error when trying to clone and build Triton today https://hud.pytorch.org/pytorch/pytorch/commit/c6d8d10b3e974019dae7ec91a85c6192c6d511fa, so let's build triton as part of the Docker image.
* The pinned commit file is moved to the Docker context at `.ci/docker/ci_commit_pins/triton.txt`, and `.github/ci_commit_pins/triton.txt` is now a soft link pointing to it
* New Docker images are built whenever the pinned commit is updated
* The build logic is in `.ci/docker/common/install_triton.sh` which copies `install_triton` step in the CI. The latter can be removed in a separate PR after this one
Pull Request resolved: https://github.com/pytorch/pytorch/pull/95233
Approved by: https://github.com/weiwangmeta, https://github.com/malfet
