Small fixes to docs structure

[giuliazanchi]

• Changed MyST syntax to render tabs
• Improved labels in the navigation tree
• Fixed two broken image links (asset manager)
• Fixed order of pages in the navigation tree (now it's the same as in https://canonical.com/multipass/docs)
• Updated conf.py to display the "Give feedback" button on all pages

NOTE: To build the docs locally, go in the /docs/ folder and run the command make run.

[giuliazanchi]

Hi @levkropp , I've rebased my commits and put everything on a branch of the main repo. The checks should pass now. Please let me know! Thank you
(The previous PR which I've closed was #3936)

EDIT: The docs build correctly, you can see them here: https://canonical-multipass--3940.com.readthedocs.build/en/3940/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.11%. Comparing base (2424799) to head (a25d7f2).
Report is 3479 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3940   +/-   ##
=======================================
  Coverage   89.11%   89.11%           
=======================================
  Files         255      255           
  Lines       14603    14603           
=======================================
  Hits        13013    13013           
  Misses       1590     1590           

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[levkropp]

Looks good! All of the fixes appear to be here and it builds and runs on my machine!