fix: show yearly labels in subscription panel for annual subscribers (#7706)

## Summary

Updates SubscriptionPanel to display yearly-appropriate labels for
annual subscribers:

- "Credits remaining this year" instead of "this month"
- "Yearly credits" instead of "Monthly credits" in the "Your plan
includes" section

## Changes

- Added `creditsRemainingThisYear` i18n key
- Added `creditsRemainingLabel` computed that switches based on
`isYearlySubscription`
- Updated `tierBenefits` to use `yearlyCreditsLabel` for annual
subscribers

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7706-fix-show-yearly-labels-in-subscription-panel-for-annual-subscribers-2d16d73d365081488552c2c0b03d862e)
by [Unito](https://www.unito.io)

src/locales/en/main.json

@@ -1933,6 +1933,7 @@
     "prepaidDescription": "Pre-paid credits",
     "prepaidCreditsInfo": "Pre-paid credits expire after 1 year from purchase date.",
     "creditsRemainingThisMonth": "Credits remaining this month",
+    "creditsRemainingThisYear": "Credits remaining this year",
     "creditsYouveAdded": "Credits you've added",
     "monthlyCreditsInfo": "These credits refresh monthly and don't roll over",
     "viewMoreDetailsPlans": "View more details about plans & pricing",