[Github] Build PGO optimized toolchain in container (#80096)

This patch adjusts the Docker container intended for CI use to contain a
PGO+ThinLTO+BOLT optimized clang. The toolchain is built within a Github
action and takes ~3.5 hours. No caching is utilized. The current PGO
optimization is fairly minimal, only running clang over hello world.
This can be adjusted as needed.