Add "Previous/Next" buttons above User-contributed Notes

[epw]

Your Godot version: 4.3

Issue description:

When there are many user-contributed notes, it makes a page of the documentation much longer and more of a pain to scroll through if you aren't interested in reading the notes. In the example which made me notice this, https://docs.godotengine.org/en/stable/getting_started/first_2d_game/05.the_main_game_scene.html#spawning-mobs , user-contributed notes are currently over three times longer than the length of that page's content.

The best fix, I think, would be to put duplicates of the Previous/Next buttons before the User-contributed notes section. The buttons should still be at the bottom of the page as well, so that it's easy to go to the next page after reading all the notes for a page.

An alternative fix could be to put User-contributed Notes into a collapsible section, preferably one that starts collapsed so the navigation buttons are easily available.

URL to the documentation page (if already existing):

Many pages, but a particularly egregious case is https://docs.godotengine.org/en/stable/getting_started/first_2d_game/05.the_main_game_scene.html#spawning-mobs

[tetrapod00]

Same problem as #9971, slightly different proposed solution.