Calculate New expires_at Using valid_for_iso From Items

[pavelbrm]

Summary

This PR is also aiming at addressing #1864.

Unlike #1870, which is very specific, this uses the maximum available valid_for_iso from the order's items instead of a hardcoded period in the query.

Note On Querying

The PR proposes a subquery for getting the period information instead of a JOIN. I ran both approaches with the planner, and think that the proposed approach is cleaner and efficient.

For comparison, this is that the PR is proposing:

SELECT
    COALESCE(last_paid_at, now()) +
    (SELECT COALESCE(MAX(valid_for_iso::interval), interval '1 month') FROM order_items WHERE order_id = $2)
AS expires_at FROM orders WHERE id = $1

A query using JOIN could be something like (which is what I checked):

SELECT COALESCE(last_paid_at, now()) + COALESCE(MAX(order_items.valid_for_iso::interval), interval '1 month') AS expires_at
FROM orders
INNER JOIN order_items ON order_items.order_id = orders.id
WHERE orders.id = $1
GROUP BY last_paid_at LIMIT 1;

The query plan in the second case contains more work, which is not necessary. I might be wrong though.

Type of Change

• Product feature
• Bug fix
• Performance improvement
• Refactor
• Other

Tested Environments

• Development
• Staging
• Production

Before Submitting

• Does your code build cleanly without any errors or warnings?
• Have you used auto closing keywords?
• Have you added tests for new functionality?
• Have validated query efficiency for new database queries?
• Have documented new functionality in README or in comments?
• Have you squashed all intermediate commits?
• Is there a clear title that explains what the PR does?
• Have you used intuitive function, variable and other naming?
• Have you requested security / privacy review if needed
• Have you performed a self review of this PR?

Manual Test Plan:

[pavelbrm]

Please note, this PR depends on #1873.