Resolve "Remove images from todos"

What does this MR do?

By default, we now strip images in the first_line_in_markdown method. This keeps images from being displayed in the one-liner of both todo and project activity panels.

Although not currently used, we allow images to be preserved with the allow_images: true options.

What are the relevant issue numbers?

Closes #31887 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [ ] Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• [ ] Conforms to the database guides