fix: use semantic figure and caption tags

[ahtesham-quraish]

What are the relevant tickets?

https://github.com/mitodl/hq/issues/9632

Description (What does it do?)

The article editor should render image+caption with semantic

and tags. These are important for screenreaders and other assistive technology. E.g.,

<figure>
  <img
    src="/shared-assets/images/examples/elephant.jpg"
    alt="Elephant at sunset" />
  <figcaption>An elephant at sunset</figcaption>
</figure>

Screenshots (if appropriate):

How can this be tested?

Just upload the image and see if it is according to semantic figure and caption

Additional Context