Add script to generate and upload rbe toolchain configs; Add rbe_preconfig repo rule to use them (#1209)

- Add script to generate and upload rbe toolchain configs
- Add rbe_preconfig which can be used to download those pre-generated RBE toolchain configs to the workspace
diff --git a/rules/WORKSPACE b/rules/WORKSPACE
new file mode 100644
index 0000000..9d067fc
--- /dev/null
+++ b/rules/WORKSPACE
@@ -0,0 +1 @@
+workspace(name = 'bazel_ci_rules')