[stronghold][bc-linter] Switch to reusable action, enable for everyone (#100737)
* Switches BC-linter to reusable action (see https://github.com/pytorch/test-infra/pull/4109)
* Removes dogfooding check / enables it for everybody
* Adds the link to the docs/user guide: https://github.com/pytorch/test-infra/wiki/BC-Linter in case of failure
To be merged on Monday, May 8 (BC linter launch date).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/100737
Approved by: https://github.com/osalpekar
