Refactor blog logic

[gtg7784]

Pull Request Summary

1. Refactor blog index page to displaying english posts when there's nothing
2. Refactor blog/[slug] page to query english post when there's nothing on the current locale
3. Refactor blog/[slug] page's fetch logic for better readability

Why?

Because there's nothing posted when I change locale to Korean
AS-IS

So, I want to displaying english posts when there's nothin on current locale
TO-BE

Check list

• contains breaking changes
• adds new feature
• modifies existing feature (bug fix or improvements)
• relies on other tasks
• documentation changes
• tested on mobile devices

This pull request makes the following changes:

Changes

• Refactor blog index page to displaying english posts when there's nothing
• Refactor blog/[slug] page to query english post when there's nothing on the current locale
• Refactor blog/[slug] page's fetch logic for better readability

[github-actions]

Visit the preview URL for this PR (updated for commit 7f3deb2):

https://astar-home--pr368-feat-astar-blog-a1i2w1g9.web.app

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[ayumitk]

LGTMT! Thank you