Throw an error if a static image doesn't exist

[julien-deramond]

Prerequisites

• I have searched for duplicate or closed feature requests
• I have read the contributing guidelines

Proposal

In HeadSEO.astro, we deduce the URL of the static images (not generated automatically) from the URL:

openresource.dev/src/components/HeadSEO.astro

Lines 8 to 10 in e313a5f

	if (openGraphData.staticImage) {
	const imagePath = canonicalURL.pathname.replaceAll(/\//g, '')
	canonicalImageSrc = new URL('images/' + (imagePath ? imagePath : 'index') + '.png', Astro.site);

However, we aren't sure that this image really exists.

The idea would be to throw an error when running npm run build to inform the developer that the image is missing.

⚠️ This would be a temporary solution waiting for #290 to be implemented. Because, in that case, this system would be useless.

Motivation and context

Avoid having Astro pages without Open Graph images.