Fix - Remove trailing slash from void elements

[Morsey187]

Description

Link to sample test page: This effects most if not all pages.
Related PRs/issues: #11592

There are quite a few changes accross multiple pages/tempaltes, although confident the changes themselves (removed trailing slash) won't effect them.

Note:

• I'm not touching React's closing tags as they're not part of SSR and those tags are rendered by React correctly (without trailing slashes) anyway the JSX syntax is just a bit different.
• There are some tags I have missed (such as hr elements) however I'm fairly confident I've addressed those in other PRs I'm about to open.

Checklist

Tests

• Is the code I'm adding covered by tests?

Changes in Models:

• Did I update or add new fake data?
• Did I squash my migration?
• Are my changes backward-compatible. If not, did I schedule a deploy with the rest of the team?

Documentation:

• Is my code documented?
• Did I update the READMEs or wagtail documentation?

Merge Method
💡❗Remember to use squash merge when merging non-feature branches into main

[mmmavis]

Awesome work. Thank you for taking the time to address these issues.