Add the 'contains_subscription' column to the Orders admin page when HPOS is enabled

[a-danae]

Fixes #499 Fixes #469

Description

This PR includes the "contains_subscription" column to the Orders list admin page when HPOS is enabled.

• Introduce WC_Subscriptions_Order::add_contains_subscription_column_content_hpos, which does the same as WC_Subscriptions_Order::add_contains_subscription_column_content but expects the arguments provided by the HPOS-specific hook.
• Hook the method mentioned above to the woocommerce_shop_order_list_table_custom_column action, which is specific for HPOS and analogous to manage_shop_order_posts_custom_column for non-HPOS.
• Hook WC_Subscriptions_Order::add_contains_subscription_column to the HPOS-specific action woocommerce_shop_order_list_table_columns. This action is analogous to the manage_edit-shop_order_columns for non-HPOS.

How to test this PR

1. Go to WooCommerce -> Settings -> Advanced -> Features. /wp-admin/admin.php?page=wc-settings&tab=advanced&section=features
2. Under Experimental features, select "High performance order storage (new)", enable "Keep the posts and orders tables in sync (compatibility mode)", and save
3. As a shopper, get the following if you don't have them already:
   • A subscription
   • A renewal for the subscription
   • A resubscribed subscription
   • An order with a non-subscription product
4. Go to WooCommerce -> Orders. /wp-admin/admin.php?page=wc-orders
5. Confirm that the column has the same behavior as when HPOS is disabled:
   • There's a column between the "Status" and "Total" columns
   • Its title is the subscription icon and has "Subscription Relationship" tooltip
   • The value in this column for each row matches the order type (Subscription, renewal, resubscription, regular order)

Regression tests

• With HPOS disabled, confirm the column continues to be displayed, and its values match the order type for each row.

Product impact

• [x] Added changelog entry (or does not apply)
• [x] Will this PR affect WooCommerce Subscriptions? yes/no/tbc, add issue ref
• [x] Will this PR affect WooCommerce Payments? yes/no/tbc, add issue ref
• [ ] Added deprecated functions, hooks or classes to the spreadsheet

[a-danae]

We'll also need to include WC_Subscriptions_Order::add_contains_subscription_hidden_field for HPOS. Planning to handle it in a separate PR to keep them small and easy to test.

Update: GH issue for this https://github.com/Automattic/woocommerce-subscriptions-core/issues/500