Replace bootstrap util with gl util in billings/subscription_table.vue

What does this MR do and why?

Re #368329 (closed)

Replaces the bootstrap util flex-lg-column with gl-lg-flex-direction-column!

Screenshots or screen recordings

No visual changes. Only the CSS class was replaced which had the same property.

Before

After

How to set up and validate locally

1. Apply this patch.

diff --git a/ee/spec/features/billings/billing_plans_spec.rb b/ee/spec/features/billings/billing_plans_spec.rb
index 7b2851f3159..dfa3f759cf7 100644
--- a/ee/spec/features/billings/billing_plans_spec.rb
+++ b/ee/spec/features/billings/billing_plans_spec.rb
@@ -118,6 +118,7 @@ def external_upgrade_url(namespace, plan)
 
     it 'displays subscription table' do
       expect(page).to have_selector('.js-subscription-table')
+      binding.pry
     end
   end
 

2. Run the billing plans spec in a headless browser and play around with the responsive styling.

CHROME_HEADLESS=0 bin/spring rspec ./ee/spec/features/billings/billing_plans_spec.rb:155

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.