Add opt_level to rust.repository_set

Author: UebelAndre

rust/extensions.bzl

@@ -169,6 +169,9 @@ _RUST_REPOSITORY_SET_TAG_ATTRS = {
     "name": attr.string(
         doc = "Name of the repository_set - if you're looking to replace default toolchains you must use the exact name you're replacing.",
     ),
+    "opt_level": attr.string_dict(
+        doc = "Rustc optimization levels. For more details see the documentation for `rust_toolchain.opt_level`.",
+    ),
     "target_compatible_with": attr.label_list(
         doc = "List of platform constraints this toolchain produces, for the particular target_triple this call is for.",
     ),