Migrate some image tags

[SSPJ]

Pull request summary

Partially does #3862.

Reminder - please do the following before assigning reviewer

• Update readme
• For frontend changes, ensure design review
• For content changes beyond typos, add Ron Bronson as a reviewer

And make sure that automated checks are ok

• fix houndci feedback
• ensure tests pass
• federalist builds
• no new SNYK vulnerabilities are introduced

[beechnut]

This is a reasonable temporary solution, but it's not a pattern I'd want us to establish for future blog posts with images. Let's see if we can iterate on this before merging.

[beepdotgov]

I've got a speculative fix for this in 3796cb7: I say "speculative", because I think the post layout isn't currently getting applied to this particular blog post. (Edit: might be related to #3849.) Let me know how you'd like me to proceed: I did a quick in-inspector test to make sure the layout works, but this will likely need visual QA/refinement once the layout's fixed. (Happy to revert the style edit, too!)

[beechnut]

Heartburn about the width-### classes aside, this looks good to merge

[beepdotgov]

Heartburn about the width-### classes aside

I knew I liked you, @beechnut

Thank you so much for the review, and for all the help getting this over the line!