Fetch prometheus from hex instead of github in bazel

as we do in Make

Author: HoloRin

workspace_helpers.bzl

@@ -174,12 +174,10 @@ erlang_lib(
         build_file = rabbitmq_workspace + "//:BUILD.osiris",
     )
 
-    github_bazel_erlang_lib(
+    hex_pm_bazel_erlang_lib(
         name = "prometheus",
-        org = "deadtrickster",
-        repo = "prometheus.erl",
-        ref = "v4.8.1",
         version = "4.8.1",
+        sha256 = "6edfbe928d271c7f657a6f2c46258738086584bd6cae4a000b8b9a6009ba23a5",
         first_srcs = [
             "src/prometheus_collector.erl",
             "src/prometheus_format.erl",