Update metagenomics-assembly tutorial

[vinisalazar]

Work for the FAIRyMAGs 2025 hackathon

Task: update assembly tutorial

Summary of changes:

• Edit data import instructions
• Add new images

Submitting as a draft for now, will mark as ready when I'm done

[vinisalazar]

@bebatut this is ready for review.

In 30def0c, I noticed that FAQ snippets like:

{% snippet faqs/galaxy/datasets_import_via_link.md %}

These don't work correctly unless there is a number list above them. Not sure if it's just a problem with my local rendering.

[vinisalazar]

Notes from catch-up meeting:

• Remove images from history - we want to avoid duplication
• Instead, can just providing json for pasting

[vinisalazar]

Had to do a force push here to remove the images from history.

[vinisalazar]

Opened #6410 in favour of this one.