chore(website): add some updates to eip4844 PR

[dionysuzx]

1. converted all headings within the doc to sentence case as per our writing style guide in the contributing manual
2. added a
   element to each screenshot/embed because visually there is not enough vertical padding in this component, it looks "squished" against the text
3. removed the code block annotation from the bullet points because semantically in markdown this should only be reserved for code blocks. also converted them with correct styling on hyphens "- " <- follow the hyphen with a space, and sentence cased
4. removed the alert thing at the bottom and combined into last sentence. generally, we actually want to stay away from using this nextra specific features. they are not "portable" / markdown compliant, and we want to be as portable as possible.