feat(ruby): Add clarification on setting context in rails (#9459)

Author: sl0thentr0py

platform-includes/enriching-events/set-context/ruby.rails.mdx

@@ -0,0 +1,15 @@
+```ruby
+Sentry.configure_scope do |scope|
+  scope.set_context(
+    'character',
+    {
+      name: 'Mighty Fighter',
+      age: 19,
+      attack_type: 'melee'
+    }
+  )
+end
+```
+
+In Rails, the best place to do this is usually in a `before_action` hook in your controller or somewhere in your model logic.
+Any data set in `configure_scope` will be shared and isolated across a single request/response cycle.