to verify that scylla builds are reproducible. the new workflow builds scylla twice with master HEAD, and compares the md5sums of the built scylla executables. it fails if the md5sum:s do not match. this workflow is triggered at 5AM every Friday. its status can be found at https://github.com/scylladb/scylladb/actions/workflows/reproducible-build.yaml after it's built for the first time. Refs #19225 Signed-off-by: Kefu Chai <kefu.chai@scylladb.com> Closes scylladb/scylladb#19409