Add ALT-texts to images where missing

For accessibility, its important to have ALT texts in all images. Including inline images.

https://learn.microsoft.com/en-us/style-guide/accessibility/graphics-design-media

"Provide brief, accurate alt text for elements other than live text, including graphics, audio, video, animations, GIFs, and pictures of text. Describe the element in a way that conveys useful information to the reader. For complex elements, link to a separate page with more details."