fix: update help links

[barredterra]

When clicking on "Help" in the navbar, some pages show links to the documentation. These have been outdated. This PR attempts to fix them.

Some pages have been renamed, most have lost the intermediate parts of the URL:

- user/manual/en/setting-up/users-and-permissions/adding-users
+ user/manual/en/adding-users

- user/manual/en/setting-up/users-and-permissions/sharing
+ user/manual/en/sharing