[CI] Add automatic retries to Buildkite workflows

Summary:
Context: https://buildkite.com/docs/pipelines/command-step#retry-attributes-automatic-retry-attributes

Should hopefully reduce the number of times that developers will need to manually restart workflows.

Test Plan: NA, see what happens

Reviewers: tomek, marcin, jon, ashoat, ginsu, rohan, varun

Reviewed By: varun

Differential Revision: https://phab.comm.dev/D6496