Refactor OpenGraph and Twitter Meta Tag Generation

[bastosmichael]

This pull request introduces enhancements to the _includes/opengraph.html template:

1. URL Concatenation - Changed how the URLs are concatenated, using the append filter for more readability and consistency.

2. OG & Twitter Image Logic - Improved the logic for setting OpenGraph and Twitter images:

   • If page.post_image exists and is not empty, it is used.
   • Otherwise, if page.image exists and is not empty, it is used.
   • If neither exist, a default image is used.

3. Description Enhancement - For both Facebook and Twitter meta tags, the description now defaults to page.description if it exists. If not, it falls back to page.title. This gives more accurate and contextually relevant descriptions.

Feedback and further suggestions are welcome!

[michaelwnau]

Reviewed.