✨feat(image shortcodes): add lazy loading, set optional alt attributes & optimise html

[welpo]

TL;DR

Enhanced image shortcodes with default lazy loading, optional alt attributes, and cleaner HTML output.

Description

This PR aims to enhance the UX and performance by introducing lazy loading to all image shortcodes and making the alt attributes optional. These changes bring about improved page loading times and give more control to users over image rendering.

Lazy loading (lazy_loading parameter):

• Lazy loading has been added to all image-related shortcodes. This defers the loading of images until they are in the viewport, improving page loading time.
• Enabled by default but can be disabled by setting the lazy_loading parameter to false.

Optional alt attributes:

• The alt attribute for images is now optional across all shortcodes. This provides greater flexibility while ensuring that best practices can still be followed.

HTML output optimisation:

• Improved the Tera templates to generate cleaner HTML by managing whitespace.