DEV: Improve add_to_serializer include_* options (#21220)

- Move the old '`define_include_method`' arg to a `respect_plugin_enabled` kwarg

- Introduce an `include_condition` kwarg which can be passed a lambda with inclusion logic. Lambda will be run via `instance_exec` in the context of the serializer instance

This is backwards compatible - old-style invocations will trigger a deprecation message

lib/discourse.rb

@@ -975,7 +975,8 @@ module Discourse
     digest = Digest::MD5.hexdigest(warning)
     redis_key = "deprecate-notice-#{digest}"
 
-    if Rails.logger && !Discourse.redis.without_namespace.get(redis_key)
+    if Rails.logger && !GlobalSetting.skip_redis? &&
+         !Discourse.redis.without_namespace.get(redis_key)
       Rails.logger.warn(warning)
       begin
         Discourse.redis.without_namespace.setex(redis_key, 3600, "x")