rabbit_boot_steps: Search boot steps only in RabbitMQ-related apps (#10064)

[Why]
We used to search for boot steps (i.e. `rabbit_boot_step` module
attributes) in every modules in every Erlang loaded applications. This
included the Erlang/OTP standard libraries and all depedencies.

This takes a looot of time. That's a lot of applications where we will
never find a boot step anyway. So most of this time is wasted.

[How]
`rabbit_misc:rabbitmq_related_module_attributes/1` was introduced for
the Feature flags subsystem for the same need to search for specific
module attributes. This function only considers the RabbitMQ core and
all plugins.

This saves a significant amount of time. And because all those modules
were already loaded when RabbitMQ search for feature flags earlier
during boot, the boot steps lookup should be quite fast.

We could consider this a change of behavior because applications which
didn't depend on the `rabbit` application are now excluded from the
search. But all plugins should depend on `rabbit`, so excluded
applications are already broken.

Author: dumbbell

deps/rabbit/src/rabbit_boot_steps.erl

@@ -7,6 +7,9 @@
 
 -module(rabbit_boot_steps).
 
+-include_lib("kernel/include/logger.hrl").
+-include_lib("rabbit_common/include/logging.hrl").
+
 -export([run_boot_steps/0, run_boot_steps/1, run_cleanup_steps/1]).
 -export([find_steps/0, find_steps/1]).
 
@@ -31,7 +34,14 @@ find_steps() ->
     find_steps(loaded_applications()).
 
 find_steps(Apps) ->
-    All = sort_boot_steps(rabbit_misc:all_module_attributes(rabbit_boot_step)),
+    T0 = erlang:timestamp(),
+    AttrsPerApp = rabbit_misc:rabbitmq_related_module_attributes(rabbit_boot_step),
+    T1 = erlang:timestamp(),
+    ?LOG_DEBUG(
+      "Boot steps: time to find boot steps: ~tp us",
+      [timer:now_diff(T1, T0)],
+      #{domain => ?RMQLOG_DOMAIN_GLOBAL}),
+    All = sort_boot_steps(AttrsPerApp),
     [Step || {App, _, _} = Step <- All, lists:member(App, Apps)].
 
 run_step(Attributes, AttributeName) ->