Add Status::MEDIA_ATTACHMENTS_LIMIT configuration constant (#30433)

spec/services/post_status_service_spec.rb

@@ -228,14 +228,15 @@ RSpec.describe PostStatusService do
     expect(media.reload.status).to be_nil
   end
 
-  it 'does not allow attaching more than 4 files' do
+  it 'does not allow attaching more files than configured limit' do
+    stub_const('Status::MEDIA_ATTACHMENTS_LIMIT', 1)
     account = Fabricate(:account)
 
     expect do
       subject.call(
         account,
         text: 'test status update',
-        media_ids: Array.new(5) { Fabricate(:media_attachment, account: account) }.map(&:id)
+        media_ids: Array.new(2) { Fabricate(:media_attachment, account: account) }.map(&:id)
       )
     end.to raise_error(
       Mastodon::ValidationError,